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Full text of "IS SP 30: National Electrical Code"

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Disclosure to Promote the Right To Information 

Whereas the Parliament of India has set out to provide a practical regime of right to 
information for citizens to secure access to information under the control of public authorities, 
in order to promote transparency and accountability in the working of every public authority, 
and whereas the attached publication of the Bureau of Indian Standards is of particular interest 
to the public, particularly disadvantaged communities and those engaged in the pursuit of 
education and knowledge, the attached public safety standard is made available to promote the 
timely dissemination of this information in an accurate manner to the public. 




Mazdoor Kisan Shakti Sangathan 
"The Right to Information, The Right to Live" 



SP 30 (2011) : National Electrical Code of India 




Jawaharlal Nehru 
'Step Out From the Old to the New' 



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BUREAU OF INDIAN STANDARDS 



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NATIONAL ELECTRICAL CODE 2011 
( First Revision ) 




BUREAU OF INDIAN STANDARDS 



SP 30: 2011 



FIRST PUBLISHED AUGUST 1985 
FIRST REVISION FEBRUARY 20 1 1 

© BUREAU OF INDIAN STANDARDS 

ICS 01.120; 91.160.01 

PRICE Rs. 4070.00 



PUBLISHED BY BUREAU OF INDIAN STANDARDS, MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR 
MARQNEWDELHI 110 002, PRINTED BY VIBA PRESS PVT. LTD., NEW DELHI 110 020 



INTRODUCTION 



India is on the path of development and its infrastructure sector has grown progressively. The buildings and 
services so constructed depend on power for their construction and effective utilization. In fact, power is one of 
the prime movers of development and electrical energy is the predominant form of energy being used due to ease 
of generation/conversion, transmission, and final utilization. 

Specific regulations to be adhered to in the supply and use of electrical energy had been laid down by the Indian 
Electricity Act, 1910 and the Indian Electricity Rules, 1956 framed thereunder. However, a need was felt to 
elaborate upon these regulations since the agencies involved have varied practices in view of their diverse interests 
and different accessibility levels to technological developments. In order to rationalize these practices, India's 
first National Electrical Code, formulated in 1985, was a compendium of several well established codes of practice 
which provided assistance on economic selection, installation and maintenance of electrical equipment employed 
in the usage of electrical energy. The code complemented and elaborated on the Indian Electricity Rules, 1956 
for the ease of application by the system engineers by recommending the best practices for electrical installations 
in a consolidated form in order to provide for unified practices and procedures along with consideration for 
safety and economic usage of energy in the design, execution, inspection and maintenance of electrical installations 
of various locations. 

During the formulation of the National Electrical Code in 1985, it was realized that the referred codes, for 
example, those on wiring practice, earthing, lightning protection etc need to be revised in line with the practice 
and technology available at that time. It had also been planned that after the relevant codes are revised, the 
National Electrical Code would also need to be revised. After the publication of NEC 1985, the referred Codes 
were revised. However, the task of revision of NEC could not be taken up in earnest immediately after the 
revision of various codes of practice. Over the years, there have been yet more changes in the technology; new 
practices have evolved and got modified. There have been tremendous socio-economic changes, and corresponding 
change in the pattern of the usage of electricity. Electricity Act 2003 has been notified and power sector reforms 
have been firmly established. During the Ninth Plan, it was realized that it is necessary to have an Energy 
Conservation Act. Accordingly, the Government has enacted the Energy Conservation Act, 2001 to meet the legal 
requirement needed to enforce energy efficiency and conservation measures. Due to all such changes, the present 
scenario is at great variance with that of 1985, when the Code was first formulated. Therefore, an urgent need was 
felt to revise the NEC at the earliest to maintain its relevance in the present context. 

The task for revision of NEC was taken up by the Electrical Installations Sectional Committee, ETD 20 considering 
the above factors. This revision follows the earlier structure of NEC, with modifications and additions being 
incorporated in line with IEC 60364 series on 'Electrical Installations' as well as the changes and developments 
that took place since the publication of NEC 1985. It is visualized that in future, further harmonization with 
international codes may be considered. 

Electrical installation should be carried out in accordance with the Indian Electricity Rules, 1956 and relevant 
regulations as amended or brought into force from time to time. All material, accessories, appliances etc., used in 
an electrical installation should conform to Indian Standards wherever they exist. There should be good 
workmanship and proper coordination and collaboration between the architect, building engineer and the electrical 
engineer from the planning stage itself. The design of electrical installation is required to take into account the 
characteristics of available supply, nature of demand, environmental conditions, type of wiring and methods of 
installations, protective equipment, emergency control, disconnecting devices, preventing of mutual influence 
between electrical and non electrical installations, accessibility etc. 

The Code is divided into eight parts, which are further divided into sections. Part 1 covers the General and 
common aspects, which would apply to all types of electrical installations. Wiring installations are an important 



aspect of any electrical installation. These have been revised to align with international practice and it is proposed 
to revise the relevant code of practice for wiring installations also. The Sections related to Earthing and Lightning 
protection have been modified and corresponding modification is also being initiated to respective codes. Aspect 
of voltage surges has also been included. Energy conservation aspects had been emphasized in NEC 1985. 
Meanwhile, Energy Conservation Act, 2001 has been notified. Therefore, energy conservation aspects have been 
further elaborated and energy audit has also been included. 

This Code excludes the requirements coming under the purview of utilities, namely, the large generating stations, 
distribution substations and associated transmission system, or captive generator sets of very large capacity. It 
covers the requirements relating to standby or emergency generating stations and captive substations intended 
for serving an individual occupancy and intended to serve a building or a group of buildings normally housed in 
and around it. It gives guidelines on layout and building construction aspects, selection of equipment, transformer 
installations, switching stations and station auxiliaries. Reference to pollution norms as laid down in Environment 
Protection Act 1986 for diesel generator sets has now been included. 

Non-industrial buildings include domestic dwellings, office buildings, shopping and commercial centers and 
institutions, recreational & assembly buildings, medical establishments, hotels and sports buildings etc. Optimum 
benefits from the use of electricity can be obtained only if the installation is of sufficient capacity and affords 
enough flexibility. Safety, economy, efficiency, reliability, convenience as well as provision for future expansion 
are major considerations in planning the electrical layout. Guidelines are provided based on general characteristics 
of installations, supply characteristics and parameters. Switchgear for control and protection, service lines, metering, 
earthing, building services, fire protection and miscellaneous provisions have been covered. Miscellaneous 
provisions include telephone wiring, call bell system, clock system, group control, audio visual systems, closed 
circuit TV where applicable, emergency lights for critical areas of the dwelling. Provision of increased number of 
points for residential units in order to accommodate the gadgets available and to avoid overloading of points by 
consumer and reference to miniature circuit breakers in addition to fuses under requirement of switchgear for 
control and protection has been made. 

Electrical networks in industrial buildings serve the purpose of distributing the required power to the consuming 
points where it is used for a multitude of purposes in the industry. The design of electrical installation in industrial 
premises is therefore more complicated than those in non-industrial buildings. Industrial installation has to take 
care of load requirements and supply limitations in a simple and economic manner, ensuring at the same time full 
protection to human life and loss of property by fire. The network layout should also facilitate easy maintenance 
and fault localization. A particular feature of electrical installations in industrial buildings is the reliability of 
supply to essential operations for which standby and emergency supply sources/networks are available. The 
needs of such systems would depend on the type and nature of the industrial works. 

Locations in industrial buildings which are by their nature hazardous, require special treatment in respect of 
design of electrical installations therein. Industrial installations have been classified depending on the specified 
criteria therein in order to help identify the specific nature of each industry and the locations therein, for assisting 
the design engineer in the choice of equipment and methods. 

Electrical installations are often required to be designed and erected for use for short periods of time ranging 
from a few hours to few months and are connected to the supply source in open ground. Such installations are 
generally unprotected from environmental hazards as compared to installations in buildings. Major risks in the 
use of power in such installation arise from short circuit resulting in fire accidents and exposure to live wire 
resulting in shock. Outdoor installations are required to comply not only with the general requirements, but also 
additional requirements regarding supply intake arrangements, control of circuits, earthing, and protection against 
overload, short circuit and earth leakage. 

There is increased use of electricity for essential purposes in agriculture with the increase in sophistication in 
organising the farm output of the country. Installations in agricultural premises are different as the external 
influences on the electrical services are quite different from those encountered elsewhere. Even though the overall 
power requirements for such installations could be small, the presence of livestock and other extraneous factors 
necessitate laying down specific requirements to ensure safety. Specific requirements of electrical installations in 
agricultural premises which include premises where livestock are present and farm produce are handled or stored 
have been covered. Agricultural processing at the farm premises has now been included. 

Any area, where during normal operations a hazardous atmosphere is likely to occur in sufficient quantity to 
constitute a hazard had to be treated in a special manner from the point of the design of electrical installation. 

iv 



Many liquids, gases and vapours which in industry are generated, processed, handled and stored are combustible. 
When ignited these may burn readily and with considerable explosive force when mixed with air in the appropriate 
proportions. With regard to electrical installations, essential ignition sources include arcs, sparks or hot surfaces 
produced either in normal operation or under specified fault conditions. NEC provides guidelines for electrical 
installations and equipment in locations where a hazardous atmosphere is likely to be present with a view to 
maximizing electrical safety. When electrical equipment is to be installed in or near a hazardous area, effort is to 
be made to locate much of the equipment in less hazardous or non-hazardous areas and thus reduce the amount 
of special equipment required. Hazardous areas can be limited in extent by construction measures, that is, walls 
or dams. Ventilation or application of protective gas also reduces the probability of the presence of explosive gas 
atmosphere so that areas of greater hazard can be transformed to areas of lesser hazard or to non-hazardous areas. 
A number of product standards offering different types of protection are available. Regulatory requirements are 
to be adhered to for such installations. Standards pertaining to classification of hazardous areas having flammable 
gases and vapours for electrical installation and guide for selection of electrical equipment for hazardous area 
have been revised and the changes have been incorporated in the NEC. 

Excessive reliance on fossil fuel resources to meet the energy requirement of the country is considered unsustainable 
in the long-run and has an adverse impact on the environment and ecology. This has resulted in the quest of 
renewable sources of energy as a viable option to achieve the goal of sustainable development. Harnessing of 
solar energy is one such area which is expected to supplement energy supply efforts. Hence a new part on solar 
photovoltaic installations has been added. 

The Code excludes guidance on tariff. Product details are also excluded from the Code as separate product 
standards are available for these. When these standards are revised subsequent to the revision of NEC, there 
could be instances where the latest Codes differ from the revised NEC. It is therefore recommended to follow the 
provisions of the latest standards/codes of practice. In order to avoid instances where the Indian Standards and 
provisions of this Code differ, attention has been drawn to the relevant standard. However, for certain provisions 
in this Code, the relevant requirements from corresponding Indian Standards have been extracted and reproduced. 
In all cases, for detailed guidance, reference should be made to the individual standard and should any contradiction 
be observed between the provisions in individual standard and those reproduced herein, the provisions of the 
former shall be considered accurate. As a general rule, technological innovations such as better materials or new 
and better method also proved as 'good practice' would first be introduced in the individual standard as appropriate 
than in the National Electrical Code. In order to keep pace with such changes and to incorporate the additional 
knowledge that will be gained through the implementation of the Code, a continuous review is envisaged. Thus, 
the users of this Code are encouraged to bring to the notice of Bureau of Indian Standards, need of modifications 
that may be required in the light of changes in technology or other factors, as this is a continuous process. 

The National Electrical Code (hereafter referred to as the Code) is intended to be advisory. It contains guidelines, 
which can be immediately adopted for use by the various interests concerned. Its provisions are presently not 
mandatory but are expected to serve as a model for adoption in the interest of safety and economy and with the 
intent to keep our electrical installation practices at par with the best practices in the world. 



COMMITTEE COMPOSITION 
Electrical Installations Sectional Committee, ETD 20 

Chairman 
SHRI N. NAGARAJAN 

Chief Engineer 
Central Public Works Department, New Delhi 



Organization 
Areva Transmission and Distribution, Noida 
BEST Undertaking, Mumbai 

BSES Rajdhani Power Ltd, New Delhi 
Central Electricity Authority, New Delhi 

Chief Electrical Inspectorate (Kerala), Thiruvananthapuram 

Chief Electrical Inspectorate (Madhya Pradesh), Bhopal 

Chief Electrical Inspectorate (Orissa), Behrampur 

Chief Electrical Inspectorate (Tamil Nadu), Chennai 

Chief Electrical Inspectorate (Uttranchal), Nainital 

Central Public Works Department, New Delhi 

Development Consultant Limited, Kolkata 



Representative(s) 

Shri Biswajit Saha 

Shri S. A. Puranik 

Shri P. R. B. Nair (Alternate) 

Shri Shantanu Dastfdar 

Shri R. K. Verma 

Shri B. R. Singh (Alternate) 

Shri K. S. Beena 

Shri K. K. Unni (Alternate) 

Shri S. S. Mujalde 

Shri A. K. Dubey (Alternate) 

Shri G. C. Choudhury 

Shri S. H. Rahman (Alternate) 

Shri R. Subramaniyan 

Shri S. Appavoo (Alternate) 

Shri Anupam Kumar 

Shri Girish Chand (Alternate) 

Shri M. K. Verma 

Shri S. Chopra (Alternate) 

Shri Jiban K. Chowdhury 

Shri Ranjit K. Das (Alternate) 

Director General Factory Advisory Services & Labour Institute, Mumbai Shri V. B. Sant 

Shri S. C. Sharma (Alternate) 



Department of Telecommunications, New Delhi 
Electrical Contractors Association of Maharashtra, Mumbai 
Electrical Contractors Association of Tamil Nadu, Chennai 
Engineers India Ltd, New Delhi 
Gujarat Electricity Board, Vadodara 



Shri Pradeep Nettur 

Shri J. S. Yadav (Alternate) 

Shri U. S. Chitre 

Shri Anil Gachke (Alternate) 

Shri A. K. Venkataswamy 

Shri T. M. Bhikkaji (Alternate) 

Shri J. M. Singh 

Shri Neeraj Sethi (Alternate) 

Shri R. O. Gandhi 

Shri K. M. Dave (Alternate) 



Indian Electrical and Electronics Manufacturers' Association, Mumbai Shri Amitabha Sarkar 

Shrimati Anita Gupta (Alternate) 



Larsen & Toubro Ltd, Chennai 

Metallurgical & Engineering Consultants (I) Ltd, Ranchi 
Ministry of Defence, New Delhi 

National Thermal Power Corporation Ltd, Noida 
Nuclear Power Corporation, Mumbai 



Shri S. Rajavel 

Shri D. Maheswaran (Alternate) 

Shri G. Mishra 

Shri A. K. Mittal 

Shri R. K. Tyagi (Alternate) 

Shri Atul Shrivastava 

Shri Rahul Aggarwal (Alternate I) 
Shri Vikram Talwar (Alternate II) 

Shri M. L. Jadhav 



VI 



Organization 
Power Grid Corporation of India Ltd, Gurgaon 

Rural Electification Corporation Ltd, New Delhi 

Siemens Ltd, Chennai 

Tariff Advisory Committee, Ahmedabad 

Tata Consulting Engineers; Mumbai 

Tamil Nadu Electricity Board, Chennai 

BIS Directorate General 



Representative(s) 

SHRr S. V. Sarma 

Shri Subir Sen (Alternate) 

Shri Dinesh Kumar 

Shri R S. Hariharan (Alternate) 

Shri T. Prabhakar 

Shri K. Gurumurthy (Alternate) 

Shri M. M. Bhuskute 

Shri P. K. Roy Chowdhury (Alternate) 

Shri Murli Muthana 

Shri Utpal Priyadarshi (Alternate) 

Shri Sukumaran 

Shri S. Kabbab (Alternate) 

Shri R. K. Trehan Scientist T' & Head (Electrotechnical) 
Representing Director General (Ex-officio Member) 



Member Secretary 

Shrimati Nishat S. Haque 

Scientist E (Electrotechnical) 



CONTENTS 



Page No. 



INTRODUCTION 
COMPOSITION 



in 
vi 



PARTI GENERAL AND COMMON ASPECTS 

Section 1 Scope of the National Electrical Code 

Section 2 Definitions 

Section 3 Graphical Symbols for Diagrams, Letter Symbols and Signs 

Section 4 Guide for Preparation of Diagrams, Charts, Tables, and Marking 

Section 5 Units and Systems of Measurement 

Section 6 Standard Values 

Section 7 Fundamental Principles 

Section 8 Assessment of General Characteristics of Buildings 

Section 9 Wiring Installations 

Section 10 Short-Circuit Calculations 

Section 1 1 Electrical Aspects of Building Services 

Section 12 Selection of Equipment 

Section 13 Erection and Pre-commissioning Testing of Installations 

Section 14 Earthing 

Section 15 Lightning Protection 

Section 1 6 Protection Against Voltage Surges 

Section 17 Guidelines for Power-Factor Improvement 

Section 18 Energy Efficiency Aspects 

Section 19 Safety in Electrical Work 

Section 20 Tables 



1 

4 
6 

13 

19 

23 

25 

27 

31 

37 

101 

110 

130 

131 

136 

163 

171 

180 

184 

186 

190 



PART 2 ELECTRICAL INSTALLATIONS IN STAND-BY GENERATING STATIONS 195 
AND CAPATIVE SUBSTATIONS 

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 201 

Section 1 Domestic Dwellings 204 

Section 2 Office Buildings, Shopping and Commercial Centres and Institutions 214 

Section 3 Recreational, Assembly Buildings 220 

Section 4 Medical Establishments 224 

Section5 Hotels 250 

Section 6 Sports Buildings 259 

Section 7 Specific Requirements for Electrical Installations in Multi-storeyed Buildings 265 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 271 

PART 5 OUTDOOR INSTALLATIONS 301 

Section 1 Public Lighting Installations 304 

Section 2 Temporary Outdoor Installations 325 

Section 3 Permanent Outdoor Installations 330 

PART 6 ELECTRICAL INSTALLATIONS IN AGRICULTURAL PREMISES 343 

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS 351 

PART 8 SOLAR PHOTOVOLTAIC (PV) POWER SUPPLY SYSTEMS 379 



NATIONAL ELECTRICAL CODE 

PART1 



SP 30: 2011 



PART 1 GENERAL AND COMMON ASPECTS 

FOREWORD 

Electrical installations require adequate planning right from concept stage to layout and designing, selection of 
proper equipment, their installation and their maintenance. Fundamental aspects of installation practice are common 
for most of the types of electrical installations. Part 1 of the National Electrical Code covers these aspects under 
its various Sections. 

An account has been taken of the Indian Standards existing on different aspects of electrical installation practice. 
However, some practices have changed over time and corresponding Codes of practice either do not exist or are 
yet to be modified. An attempt has been made through this Code to refer to the present good practices. A reference 
has also been made to product standards in order to inform the user of the Code about the availability and 
desirability to use them. 

Aspects concerning specific occupancies are covered in other Parts and Sections of this Code. The fundamental 
principles of installation practice covered under Part 1 of this Code generally apply, unless modified or 
supplemented by subsequent Parts. This Part 1 would also be a useful reference for occupancies not explicitly 
covered by the scope of subsequent Parts of the Code. 

PART 1 GENERAL AND COMMON ASPECTS 3 



SP 30 : 2011 



SECTION 1 SCOPE OF THE NATIONAL ELECTRICAL CODE 



FOREWORD 

Each Part/Section of the National Electrical Code 
covers the requirements relating to electrical 
installations in specific occupancies. The fundamental 
and general principles governing electrical installation 
practice together with common aspects applicable to 
all types of installations has been brought out in a 
separate Part in order to serve as a reference document 
on such matters. 

The details enumerated in this Part are generally 
applicable to all types of occupancies and are to be 
read as modified or supplemented with the information 
provided in the relevant Parts of the Code. 

Effort has been made to make this part self-contained, 
so that users of the Code can derive utmost advantage 
in using it for application in the field even for 
occupancies not explicitly covered by the scope of 
subsequent Parts of the Code. Efforts have also been 
made to ensure that all the relevant details required for 
the understanding of the Code are available to the extent 
possible within Part 1 and effort has been made to keep 
the references of individual standards to the minimum. 

1 SCOPE 

This Part 1 /Section 1 of the Code describes the scope 
of the National Electrical Code. 

2 REFERENCES 

The National Electrical Code takes into account the 
stipulations in several Indian Standards dealing with 
the various aspects relating to electrical installation 
practice. Several product standards also exist, and 
compliance with relevant Indian Standards is 
desirable. It is therefore recommended that individual 
Parts/Sections of the Code should be read in 
conjunction with the relevant Indian Standards. List 
of such Indian Standards is given at relevant Part/ 
Section of the Code. 

At the time of publication, the editions indicated were 
valid. All standards are subject to revision, and parties 
to agreements based on this standard are encouraged 
to investigate the possibility of applying the most recent 
editions of the standards. 

3 SCOPE OF THE NATIONAL ELECTRICAL 
CODE 

3.1 The National Electrical Code covers the following: 

a) Standard good practices for selection of 



various items of electrical equipment forming 
part of power systems; 

b) Recommendations concerning safety and 
related matter in the wiring of electrical 
installations of buildings or industrial 
structures, promoting compatibility between 
such recommendations and those concerning 
the equipment installed; 

c) General safety procedures and practices in 
electrical work; and 

d) Additional precautions to be taken for use of 
electrical equipment for special environmental 
conditions like explosive and active 
atmosphere. 

3.2 The Code applies to electrical installations such as 
those in: 

a) Standby/emergency generating plants and 
building substations; 

b) Domestic dwellings; 

c) Office buildings, shopping and commercial 
centres and institutions; 

d) Recreation and other public premises; 

e) Medical establishments; 

f) Hotels; 

g) Sports buildings; 
h) Industrial premises; 

j) Temporary and permanent outdoor 

installations; 
k) Agricultural premises; 
m) Installations in hazardous areas; and 
n) Solar photovoltaic installations. 

NOTES 

1 Any type of installation not covered by the above shall be 
classified in the group which most nearly resemble its existing 
or proposed use. 

2 Where change in the occupancy places it under the scope 
of a different Section of the Code, the same installation shall 
be made to comply with the requirements of the Code for 
the new occupancy. 

33 The Code applies to circuits other than the internal 
wiring of apparatus. 

3*4 The Code does not apply to traction, motor vehicles, 
installations in rolling-stock, on board-ships, aircraft 
or installations in underground mines. 

3.5 The Code covers only electrical aspects of lightning 
protection of buildings and in so far as the effects of 
lightning on the electrical installations are concerned. 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 

It does not cover lightning protection aspects from b) Power generation and transmission for such 

structural safety point of view. systems. 

3.6 The Code is also not intended to apply to, 3.7 The Code also does not cover guidelines on the 

. _ .,..,. „ lt . payment for electrical work done in installations, 
a) Systems of distribution of energy to public; 

and 



PART 1 GENERAL AND COMMON ASPECTS 



SP 30 : 2011 



SECTION 2 DEFINITIONS 



FOREWORD 

Each Part of the Code gives, where necessary, 
definitions of terms and phrases relevant for the 
comprehension of the requirements stipulated therein. 
Users may find it convenient to refer to a detailed list 
of terms and their definitions contained in this section 
that are relevant to electrical installation practice. It 
may however be noted that for further guidance, 
recourse should be made to IS 1885 (series) on 
electrotechnical vocabulary containing a compendium 
of terms in the field. 

The definitions contained in the Code are based on the 
current international terminology as far as possible. 
Some definitions are based on the terminology drawn 
up by the relevant expert groups under the 
Electrotechnical Division Council with the object of 
striking a correct balance between absolute precision 
and simplicity. The principal object of this exercise is to 
provide definitions which are sufficiently clear so that 
each term is understood with the same meaning by all 
concerned. It may sometimes be felt that the definitions 
are not identical with those which may be found in other 
publications designed with different objectives and for 
other readers. Such differences are inevitable and should 
be accepted in the interest of clarity. 

1 SCOPE 

This Part 1/Section 2 of the Code covers definitions of 
terms. 

2 REFERENCES 

A list of Indian Standards on electrotechnical 
vocabulary relevant for the purpose of the Code is given 
at Annex A. 

3 TERMINOLOGY 

3.0 For the purpose of the National Electrical Code, 
the following definitions shall apply, in addition to 
those contained in individual Parts/Sections and 
relevant Indian Standards. 

3.1 Fundamental Definitions 

3.1.1 Capacitor — A system of two conductors (plates) 
separated over the extent of their surfaces by an 
insulation medium which is capable of storing electrical 
energy as electrical stress. 

3.1.2 Conductor — A substance or body which allows 
current of electricity to pass continuously. 

3.1.3 Dielectric — A material medium in which an 
electric field can exist in a stationary state. 



3.1.4 Electrode — A conducting element used for 
conveying current to and from a medium. 

3.1.5 Current — The elementary quantity of electricity 
flowing through a given section of a conductor divided 
by the corresponding indefinitely small time. 

3.1.6 Electric Circuit — An arrangement of bodies or 
media through which a current can flow. 

3.1.7 Electric Current — The movement of electricity 
in a medium or along a circuit. The direction of the 
current is accepted as opposite to that of the motion of 
negative electricity. 

3.1.8 Voltage, Potential Difference — The line of 
integral from one point to another of an electric field, 
taken along a given path. 

3.1.9 Arc — A luminous discharge of electricity across 
a gas, characterized by a large current and a low voltage 
gradient, often accompanied by partial volatilization 
of the electrodes. 

3.1.10 Flashover — The passage of a disruptive 
discharge round in insulating material. 

3.1.11 Spark — A brilliantly luminous phenomenon 
of short duration which characterized a disruptive 
discharge. 

3.1.12 Connection of Circuits 

3.1.12.1 Series — An arrangement of elements so that 
they all carry the same current or flux. 

3.1.12.2 Parallel — An arrangement of elements so 
that they all carry a portion of total current or flux 
through them 

3.1.12.3 Series parallel — An arrangement of elements 
of which some are connected in series and others in 
parallel. 

3.1.13 Earth Fault — Accidental connection/contact 
of a conductor to earth. When the impedance is 
negligible, the connection is called a dead earth. 

3.1.14 Earth Leakage Current — The current flowing 
to earth on account of imperfect insulation. 

3.1.15 Insulation Fault — An abnormal decrease in 
insulation resistance. 

3.1.16 Overload — Operating conditions in an 
electrically undamaged circuit which causes an 
overcurrent. 

3.1.17 Short-circuit — The intentional or accidental 
connection of two points of a circuit through a 
negligible impedance. The term is often applied to the 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



group of phenomena which accompany a short circuit 
between points at different potentials. 

3.2 Equipment 

3.2.1 Electrical Equipment — The electrical machines, 
apparatus and circuits forming part of an electrical 
installation or a power system. 

NOTES 

1 Outdoor electrical equipment are those suitable for 
installation in open air. 

2 For the purpose of this Code, the term electrical equipment 
can in general be used to any item used for such purposes as 
generation, conversion, transmission, distribution or utilization 
of electrical energy such as machines, transformers, apparatus, 
measuring instruments, protective devices, wiring material and 
appliances. 

3.2.2 Current Using Equipment — Equipment intended 
to convert electrical energy into another form of energy, 
for example, light, heat or motive power. 

3.2.3 Portable Equipment — Equipment which is 
moved while in operation or which can easily be moved 
from one place to another while connected to the 
supply. 

3.2.4 Hand- he Id Equipment — Portable equipment 
intended to be held in the hand during normal use, in 
which the motor, if any, forms an integral part of the 
equipment. 

3.2.5 Stationary Equipment — Either fixed equipment 
or equipment not provided with a carrying handle and 
having such a mass that it cannot easily be moved. 

3.2.6 Fixed Equipment — Equipment fastened to a 
support or otherwise secured in a specific location. 

3.2.7 Generator — A machine for converting mechanical 
energy into electrical energy. 

3.2.8 Electric Motor — A machine for converting 
electrical energy into mechanical energy. 

3.2.9 Induction Motor — An alternating current motor 
without a commutator in which one part only, the rotor 
or a stator, is connected to the supply network, the other 
working by induction. 

3.2.10 Motor Generator Set — A machine which 
consists of an electric motor mechanically coupled to 
a generator. 

3.2.11 Auto-transformer — A transformer in which the 
primary and secondary windings have common part 
or parts. 

3.2.12 Transformer — A piece of apparatus, without 
continuously moving parts, which by electromagnetic 
induction transforms variable voltage and current in 
one or more other windings usually at different values 
of voltage and current and at the same frequency. 



3.2.13 Relay (Including Gas-operated Relay) — A 
device designed to produce sudden pre-determined 
changes in one or more physical systems on the 
appearance of certain conditions in the physical system 
controlling it. 

3.2.14 Switchgear and Controlgear — A general term 
covering switching devices and their combination with 
associated control, measuring, protective and 
regulating equipment, also assemblies of such devices 
and equipment with associated inter-connections, 
accessories, enclosures and supporting structures 
intended in principle for use in connection with 
generation, transmission, distribution and conversion 
of electric energy. Controlgears are switching devices 
intended in principle for the control of electrical energy 
consuming equipment. 

3.2.15 Switch (Mechanical) — A mechanical switching 
device capable of making carrying and breaking 
currents under normal circuit conditions which may 
include specified operating overload conditions and 
also carrying for a specified time currents under 
specified abnormal circuit conditions such as those of 
a short-circuit. 

3.2.16 Switch-fuse — A switch in which one or more 
poles have a fuse in series in a composite unit. 

3.2.17 Fuse-switch — A switch in which a fuse-link 
or a fuse-carrier with fuse-link forms the moving 
contact of the switch. 

3.2.18 Circuit-Breaker (Mechanical) — A mechanical 
switching device capable of making carrying and 
breaking currents under normal circuit conditions and 
also making, carrying for a specified time and breaking 
currents under specified abnormal circuit conditions 
such as those of a short-circuit. 

3.2.19 Fuse — device that, by the fusing of one or 
more of its specially designed and proportioned 
components, opens the circuit in which it is inserted 
by breaking the current when this exceeds a given value 
for a sufficient time 

NOTE — The fuse comprises all the parts that form the 
complete device. 

3.2.20 Enclosed Distribution Fuse-board — An 
enclosure containing bus-bars, with fuses, for the 
purposes of protecting, controlling or connecting more 
than one outgoing circuit fed from one or more 
incoming circuits. 

3.2.21 Enclosed Fuse-link — Fuse-link in which the 
fuse-element is totally enclosed, so that during 
operation within its rating it cannot produce any 
harmful external effects, for example, due to 
development of an arc, the release of gas or the ejection 
of flame or metallic particles. 



PART 1 GENERAL AND COMMON ASPECTS 



SP 30 : 2011 



3.2.22 Fuse- link — Part of a fuse including the fuse- 
elements) intended to be replaced after the fuse has 
operated. 

3.2.23 Miniature Circuit-breaker — A compact 
mechanical device for making and breaking a circuit 
both in normal conditions and in abnormal conditions 
such as those of overcurrent and short-circuit. 

3.2.24 D-Type Fuse — A non-interchangeable fuse 
comprising a fuse-base a screw type fuse-carrier, a 
gauge piece and a fuse-link. 

3.2.25 Distribution Pillar — A totally enclosed 
structure cubicle containing bus-bars connected to 
incoming and outgoing distribution feeders controlled 
through links fuses. 

3.2.26 Interconnecting Bus-bar — A conductor other 
than cable, used for external connection between 
terminals of equipment. 

3.2.27 Bimetallic Connector — A connector designed 
for the purpose of connecting together two or more 
conductors of different materials (normally copper and 
aluminium) for preventing electrolytic corrosion. 

3.2.28 Fuse-element (Fuse-wire in Rewirable Fuse) — 
That part of a rewirable fuse, which is designed to melt 
when the fuse operates. 

3.2.29 Fuse-base (Fuse-mount) — The fixed part of a 
fuse provided with contacts and terminals for 
connection to the system. The fuse-base comprises all 
the parts necessary for insulation. 

3.2.30 Fuse-carrier — The movable part of a fuse 
designed to carry a fuse-link. The fuse-carrier does not 
include any fuse-link. 

3.2.31 Lightning Arrester (Surge Diverter) — A device 
designed to protect electrical apparatus from high 
transient to protect electrical apparatus from high 
transient voltage and to limit the duration and 
frequently the amplitude of follow-current. The term 
'lightning arrester' includes any external series gap 
which is essential for the proper functioning of the 
device as installed for service, regardless of whether 
or not it is supplied as an integral part of the device. 

3.3 Wiring Practice 

3.3.1 Accessory — Any device, associated with the 
wiring and electrical appliance of an installation, for 
example, a switch, a fuse, a plug, a socket-outlet, a 
lamp holder, or a ceiling rose. 

3.3.2 Apparatus — Electrical apparatus including all 
machines, appliances and fittings in which conductors 
are used for of which they may form a part. 

3.3.3 Aerial Conductor — Any conductor which is 



supported by insulators above the ground and is directly 
exposed to the weather. 

NOTE — The following four classes of aerial conductors are 
recognized: 

a) Bare aerial conductors, 

b) Covered aerial conductors, 

c) Insulated aerial conductors, and 

d) Weatherproof neutral-screened cable. 

3.3.4 Bunched — Cables are said to be 'bunched' when 
two or more are contained within a single conduit, duct 
or groove or, if not enclosed, are not separated from 
each other. 

3.3.5 Cable — A length of single-insulated conductor 
(solid or stranded), or two or more such conductors, 
each provided with its own insulation, which are laid 
up together. The insulated conductor or conductors may 
or may not be provided with an overall mechanical 
protective covering. 

3.3.6 Cable, Armoured — A cable provided with a 
wrapping of metal (usually in the form of tape or wire) 
serving as a mechanical protection. 

3.3.7 Cable, Flexible — A cable containing one or more 
cores, each formed of a group of wires, the diameters 
of the cores and of the wires being sufficiently small 
to afford flexibility. 

3.3.8 Circuit — An arrangement of conductor or 
conductors for the purpose of conveying energy and 
forming a system or a branch of a system. 

3.3.9 Circuit, Final, Sub — An outgoing circuit 
connected to one-way distribution fuse-board and 
intended to supply electrical energy at one or more 
points to current-using appliances, without the 
intervention of a further distribution fuse-board other 
than a one-way board. It includes all branches and 
extensions derived from that particular way in the 
board. 

3.3.10 Cleat — An insulated incombustible support 
normally used for insulated cable. 

3.3.11 Conductor, Bare — A conductor not covered 
with insulating material. 

3.3.12 Conductor, Earthed — A conductor with no 
provision for its insulation from earth. 

3.3.13 Conductor, Insulated — A conductor adequately 
covered with insulating material of such quality and 
thickness as to prevent danger. 

3.3.14 Connector Box or Joint Box — A box forming 
a part of wiring installation provided to contain joints 
in the conductors of cables of the installation. 

3.3.15 Conductor for Portable Appliances — A 
combination of a plug and socket arranged for 



8 



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SP 30: 2011 



attachment to a portable electrical appliance or to a 
flexible cord. 

3.3.16 Consumer's Terminals — The ends of the 
electrical conductors situated upon any consumer's 
premises and belonging to him at which the supply of 
energy is delivered from the service line. 

3.3.17 Cord, Flexible — A flexible cable having 
conductor of small cross-sectional area. Two flexible 
cords twisted together are known as 'Twin Flexible 
Cord'. 

NOTE — For the maximum diameter and minimum number 
of wires for flexible cord, see relevant standard. 

3.3.18 Cut-out — Any appliance for automatically 
interrupting the transmission of energy through any 
conductor when the current rises above a 
predetermined amount, for example, fusible cut-out. 

3.3.19 Dead — At or about earth potential and/or 
disconnected from any live system. 

3.3.20 Direct Earthing System — A system of earthing 
in which the parts of an installation are so earthed as 
specified but are not connected within the installation 
to the neutral conductor of the supply system or to earth 
through the trip coil of an earth leakage circuit-breaker. 

3.3.21 Distribution Fuse-board — An assemblage of 
parts including one or more fuses arranged for the 
distribution of electrical energy to final sub-circuits. 

3.3.22 Earth — A connection to the general mass of 
earth by means of an earth electrode. An object is said 
to be 'earthed' when it is electrically connected to an 
earth electrode; and a conductor is said to be 'solidly 
earthed' when it is electrically connected to earth 
electrode without a fuse, switch, circuit-breaker, 
resistance or impedance in the earth connection. 

3.3.23 Earth Continuity Conductor — The conductor, 
including any clamp, connecting to the earthing lead 
or to each other those parts of an installation which 
are required to be earthed. 

3.3.24 Earth Electrode — A metal plate, pipe or other 
conductor electrically connected to the general mass 
of the earth. 

3.3.25 Earthing Lead — The final conductor by which 
the connection to the earth electrode is made. 

3.3.26 Fitting, Lighting — A device for supporting or 
containing a lamp or lamps (for example, fluorescent 
or incandescent) together with any holder, shade, or 
reflector, for example, a bracket, a pendant with ceiling 
rose, or a portable unit. 

3.3.27 Flammable — A material capable of being easily 

ignited. 



3.3.28 Disconnector — A device used to open (or close) 
a circuit when either negligible current is interrupted 
(or established) or when the significant change in the 
voltage across the terminal of each of the pole of the 
disconnector occurs; in the open position it provides 
an isolating distance between the terminals of each 
pole. 

3.3.29 Double Insulation 

a) Of a conductor — A conductor is said to have 
double insulation when insulating material 
intervenes not only between the conductor and 
its surrounding envelope (if a cable) or 
immediate support (if bare), but also between 
the envelope or support and earth. 

b) Of an appliance — An appliance having 
accessible metal part is doubly insulated when 
protective insulation is provided in addition 
to the normal functional insulation, in order 
to protect against electric shock in case of 
breakdown of the functional insulation. 

3.3.30 Live or Alive — Electrically charged so as to 
have a potential difference from that of earth. 

3.3.31 Multiple Earthed Neutral System — A system 
of earthing in which the parts of an installation, 
specified, to be earthed are connected to the general 
mass of earth and, in addition, are connected within 
the installation to the neutral conductor of the supply 
system. 

3.3.32 Neutral or Neutral Conductor — Includes the 
neutral conductor of a three-phase four-wire system, 
the conductor of a single-phase or dc installation which 
is earthed by the supply undertaking (or otherwise at 
the source of the supply), and the middle wire or 
common return conductor of a three- wire dc or single- 
phase ac system. 

3.3.33 Point — A point shall consist of the branch 
wiring from the branch distribution board, together 
with a switch as required, as far as and including the 
ceiling rose or socket-outlet or suitable termination. A 
three-pin socket-outlet point shall include, in addition, 
the connecting wire or cable from the earth pin to the 
earth stud of the branch distribution board. 

3.3.34 Service — The conductors and equipment 
required for delivering energy from the electric supply 
system to the wiring system of the premises served. 

3.3.35 Socket-outlet and Plug — A device consisting 
of two portions for easily connecting portable lighting 
fittings or other current-using appliances/devices to the 
supply. The socket-outlet is an accessory having socket 
contacts designed to engage with the pins of a plug 
and having terminals for the connection of cable(s). 



PART 1 GENERAL AND COMMON ASPECTS 



SP 30: 2011 



The plug portion has pins designed to engage with the 
contacts of a socket-outlet, also incorporating means 
for the electrical connection and mechanical retention 
of flexible cable(s). 

3336 Switchboard — An assemblage of switchgear 
with or without instruments but the term does not apply 
to a group of local switches or a final sub-circuit where 
each switch has its own insulating base. 

3337 Voltage, Low - — The voltage which does not 
normally exceed 250 V. 

3338 Voltage, Medium — The voltage which normally 
exceeds 250 V but does not exceed 650 V. 

3339 Voltage, High — The voltage which normally 
exceeds 650 V (but less than 33 kV). 

3.3,40 Voltage, Extra- High — The voltage exceeding 
33 kV under normal conditions. 

NOTE — The Indian Electricity Rules, 1956 define four ranges 
of voltages, namely, low (up to 250 V), medium (250-650 V), 
high (650 V-33 kV) and extra-high (greater than 33 kV). The 
definitions given in 3.3.37 to 3.3.40 are based on the provisions 
of IE Rules. It may however, be noted that voltage ranges as 
defined internationally are at variance with the above 
definitions. 

3.4 Miscellaneous Terms 

3.4.1 Building — Any structure for whatsoever purpose 
and of whatsoever materials constructed and every part 
thereof whether used as human habitation or not and 
includes foundation, plinth, walls, floors, roofs, 
chimneys, plumbing and building services, fixed 
platforms, verandah, balcony, cornice or projection, 
part of a building or any thing affixed thereto or any 
wall enclosing or intended to enclose any land or space 
and signs and outdoor display structures. Tents, 
shamianahs, tarpaulin shelters, etc, erected for 
temporary of the Authority shall not be considered as 
building. 

3.4.2 Occupancy or Use Group — The principal 
occupancy for which a building or a part of a building 
is used or intended to be used; for the purposes of 
classification of a building according to occupancy, 
an occupancy shall be deemed to include the subsidiary 
occupancies which are contingent upon it 

3.4.3 Room Height — The vertical distance measured 
from the finished floor surface to the finished ceiling 
surface. Where a finished ceiling is not provided, the 
underside of the joints or beams or tie beams shall 
determine the upper point of measurement for 
determining the head room. 

3.4.4 Impulse — Usually an aperiodic transient voltage 
or current which rises rapidly to a peak value and then 
falls, generally more slowly, to zero. Ideally it 



approximates a double exponential form. Other forms 
are sometimes used for special purposes. 

3.4.5 Clearance — The distance between two 
conducting parts along a string stretched the shortest 
way between these conducting parts. 

3.4.6 Creepage Distance — The shortest distance 
between two conducting parts along the surface of the 
insulating material or along the joint of two insulating 
bodies. 

3.4.7 Simultaneously Accessible Parts — Conductors 
or conductive parts that can be touched simultaneously 
by a person or where applicable by livestock. 

NOTE — Simultaneously accessible parts may be; 

a) live parts, 

b) exposed conductive parts, 

c) extraneous conductive parts, 

d) protective conductors, and 

e) earth electrodes. 

3.4.8 Arm } s Reach — A zone extending from any point 
on a surface where persons usually stand or move about 
to the limits which a person can reach with the hand in 
any direction without assistance. 

3.4.9 Enclosure — A part providing protection of 
equipment against certain external influences and, in 
any direction, protection against direct contact. 

3.4.10 Barrier — A part providing protection against 
direct contact from any usual direction of access. 

3.4.11 Obstacle — A part preventing unintentional 
direct contact, but not preventing deliberate action. 

3.4.12 Leakage Current (in an Installation) — A 
current which flows to earth or to extraneous 
conductive parts in a circuit in the absence of a fault. 

NOTE — This current may have a capacitive component 
including that resulting from the deliberate use of capacitors. 

3.4.13 Nominal Voltage (of an Installation) — Voltage 
by which an installation or part of an installation is 
designated. 

NOTE — The actual voltage may differ from the nominal 
voltage by a quantity within permitted tolerances. 

3.4.14 Supply Terminals — The point at which a 
consumer received energy. 

3.4.15 Service Line, Service — A line for connecting a 
current consuming installation to the distribution 
network. 

3.4.16 Distribution Undertaking — The party 
supplying electricity to consumers entirely from 
external sources of power via a distribution network. 

3.4.17 Consumer or Customer — The party who 



10 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



receives electricity from the supply or distribution 
undertaking for his own needs or for further 
distribution. 

3.4.18 Demand — The magnitude of electricity supply, 
expressed in kW or kVA. 

3.4.19 Installed Load — The sum of the rated inputs 
of the electrical apparatus installed on the consumer's 
premises, 

3.4.20 Connected Load — The part of the installed 
load of consumer supplied by the supply undertaking. 

3.4.21 Kilowatthour Rate (kWh Rate) — The amount 
to be paid per unit of energy (kWh) consumed. 

3.4.22 Meter Rent — An amount to be paid for a 
specified period for metering, and associated 
equipment installed. 

3.4.23 Tariff — A statement setting out the components 
to be taken into account and the methods to be 
employed in calculating the amounts to be charged by 
the supply/distribution undertaking to the consumer, 
according to the characteristics of the supply. 

3.4.24 Domestic Tariff — A tariff applicable 
particularly or exclusively to domestic consumers. 



3.4.25 Industrial Tariff — A tariff applicable 
exclusively to industrial consumers. 

3.4.26 Lighting Tariff — A tariff applicable to 
electricity supplies taken mainly for lighting and other 
small appliances, for example, fans and radios. 

3.4.27 Heating Tariff — A tariff applicable to electricity 
supplies taken for space heating or for thermal 
applications or for both. 

3.4.28 Power Factor Clause — A clause setting out 
increase in charges to be applied if the ratio of the kWh 
to kVAh consumed by a consumer during a specified 
period below a set limit; the same clause may provide 
for a decrease in charges in the opposite case. 

NOTE — The power factor is generally measured by the ratio 
of kWh to kVAh consumed during the specified period. 

3.4.29 Load Factor — The ratio, expressed as a 
numerical value or as a percentage, of the energy 
consumption within a specified period (year, month, 
day, etc) to the energy consumption that would result 
from continuous use of the maximum kW demand 
occurring within the same period. 

NOTE — The load factor for a given demand is also equal to 
the ratio of the utilization time to the time in hours within the 
same period. 



ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS ON ELECTROTECHNIC AL VOCABULARY 



IS No. 

1885 
(Part 1) : 1961 
(Part 8) : 1986 

(Part 9): 1992/ 

IEC 60050 (446) 

1983 

(Part 10) : 1993/ 

IEC 60050 (448) 

1986 

(Part 11): 1966 

(Part 14) : 1967 

(Part 15) : 2003/ 

IEC 60050 (481) 

1996 

(Part 16/Sec 1) : 

1968 



Title 

Electrotechnical vocabulary: 

Fundamental definitions 

Secondary cells and batteries (first 

revision) 

Electrical relays (second revision) 



Power system protection (first 
revision) 

Electrical measurements 
Nuclear power plants 
Primary cells and batteries (first 
revision) 

Lighting, Section 1 General aspects 



IS No. 

(Part 16/Sec 2) : 
1968 

(Part 16/Sec 3) : 

1967 

(Part 17) : 1979 

(Part 27): 1993/ 

IEC 60050 (551) 

1982 

(Part 28) : 1993/ 

IEC 60050 (321) 

1986 

(Part 29): 1971 

(Part 30): 1971 



Title 

Lighting, Section 2 General 

illumination, lighting fittings and 

lighting for traffic and signalling 

Lighting, Section 3 Lamps and 

auxiliary apparatus 

Switchgear and controlgear (first 

revision) 

Power electronics (second 

revision) 

Instrument transformers (first 
revision) 

Mining terms 

Overhead transmission and 

distribution of electrical energy 



PART 1 GENERAL AND COMMON ASPECTS 



11 



SP 30:- 2011 



IS No. 

(Part 32) : 1993/ 

IEC 60050 (461): 

1984 

(Part 34) : 1972 

(Part 35) : 1993/ 

IEC 60050 (411); 

1996 

(Part 37) : 1993/ 

IEC 60050 (691): 

1973 

(Part 38): 1993/ 

IEC 60050 (421): 

1990 

(Part43):1977 

(Part 51): 1993/ 
IEC 60050 (841) : 
1983 

(Part 53) : 1980 
(Part 54) : 1993/ 
IEC 60050 (471): 
1984 

(Part 55): 1981 
(Part 57): 1993/ 
IEC 60050 (131): 
1978 

(Part 60) : 1993/ 
IEC 60050 (426) : 
1990 

(Part61):1985 
(Part 62); 1993/ 
IEC 60050 (212): 
1990 

(Part 69): 1993/ 
DEC 60050 (602) : 
1993 

(Part 70) : 1993/ 
IEC 60050 (604) : 
1987 



Title 
Electric cables (first revision) 



Cinematography 

Rotating machinery (first revision) 



Part 37 Tariffs for electricity (first 
revision) 

Power transformers and reacto 
(second revision) 

Electrical equipment used in 

medical 

Industrial electro-heating 



Mica 

Insulators (first revision) 



Electric fans 

Electric and magnetic circuits (first 

revision) 

Electrical apparatus for explosive 
atmospheres (first revision) 

Nuclear medical instruments 
Solid insulating materials (first 
revision) 

Generation, transmission and dis- 
tribution of electricity — Generation 

Generation, transmission and dis- 
tribution of electricity — 
Operation 



IS No. 

(Part 71): 1993/ 

IEC 60050 (605) : 

1983 

(Part72):1993/ 

IEC 60050 (101): 

1977 

(Part73/Secl): 

1993/IEC60050 

(111-1): 1984 

(Part73/Sec2): 

1993/IEC 60050 

(111-2): 1984 

(Part73/Sec3): 

1993/IEC 60050 : 

(111-3): 1977 

(Part 74): 1993/ 

IEC 60050 (151): 

1978 

(Part 75): 1993/ 

IEC 60050 (351): 

1975 

(Part 77): 1993/ 

IEC 60050 (466) : 

1990 

(Part78):1993/ 

IEC 60050 (601): 

1985 

(Part 79): 1993/ 

IEC 60050 (603) : 

1986 

(Part 80): 1994/ 

IEC 60050 (301) : 

1983 

(Part 81): 1993/ 

IEC 60050 (302) : 

1983 



Title 
Generation, transmission and 
distribution of electricity — 
Substations 
Mathematics 



Physics and chemistry, Section 1 
physical concepts 

Physics and chemistry — Section 
2 Electrotechnical concepts 

Physics and chemistry — Section 3 

Concepts related to quantities and 

units 

Electrical and magnetic devices 



Automatic control 



Overhead lines 



Generation, transmission and 
distribution of electricity — 
General 

Generation, transmission and 
distribution of electricity — Power 
system planning and management 
General terms on measurements 
in electricity 

Electrical measuring instruments 



12 



NATIONAL ELECTRICAL CODE 



SF 30: 2011 



SECTION 3 GRAPHICAL SYMBOLS FOR DIAGRAMS, LETTER 

SYMBOLS AND SIGNS 



FOREWORD 

Several graphical symbols are used for installation 
diagrams. Considerable amount of standardization has 
been achieved in the field of 

symbols for electrotechnology that it is now possible 
to device electrical network schematics using them so 
that these schematic diagrams could be uniformly 
understood by all concerned. 

The symbols contained in this Section of the Code have 
been drawn up by individual expert groups under the 
Electrotechnical Division Council. They represent a 
consensus of opinion in the discipline and are 
recommended for direct adoption. Assistance has also 
been drawn from International Electrotechnical 
Commission (IEC) database IEC 60617 'Graphical 
symbols for diagrams'. 

It has also been felt essential for the purposes of this 
Section to draw the attention of practicing engineers 
to standardized letter symbols and signs. 

1 SCOPE 

This Part 1 /Section 3 of the Code covers graphical 
symbols for diagrams, letter symbols and signs which 
may be referred to for further details. 

2 REFERENCES 

A list of relevant Indian Standards on graphical 
symbols is given at Annex A. 

3 GRAPHICAL SYMBOLS 

3.0 For the purposes of the Code, the graphical symbols 
given below shall apply. 

NOTE — A list of Indian Standards on graphical symbols used 
in electrotechnology relevant to the Code is given in Annex A. 

3.1 Fundamental Symbols 
3.1.1 Direct Current 



3.1.2 Alternating Current, General Symbol 

a) Alternating current, single-phase, 50 Hz 

r\jsoHz 



b) Alternating current, three-phase, 415 V. 
50 Hz 



/"\ J 50Hz « 
r \-/ 415V 



c) Alternating current, three-phase with neutral. 
50 Hz 



3.1.3 Neutral 



3nT\J 50Hz 



N 



3.1.4 Positive Polarity 

+ 

3.1.5 Negative Polarity 

3.1.6 Direct Current, 2 Conductors 110 V 

2 110V 

3.1.7 Direct Current, 3 Conductors including Neutral, 
220V 

2N _ 220V 

3.1.8 Underground Cable 



3.1.9 Overhead Line 



3.1.10 Winding, Delta 



3.1.11 Winding, Star 



3.1.12 Terminals 



A 

Y 



PART 1 GENERAL AND COMMON ASPECTS 



13 



SP 30 : 2011 

3.1.13 Resistance/Resistor 

3.1.13.1 Variable resistor 



*■ 



3.1.14 Impedance 



3.1.15 Inductance/Inductor 



3.1.16 Winding 

3.1.17 Capacitance, Capacitor 

3.1.18 Earth 



3.1.19 Fault 



f 



3.2 Equipment 

3.2.1 Flexible Conductor 



3.2.2 Generator 



© 



3.2.2.1 AC generator 



3.2.2.2 DC generator 





3.2.3 Motor 



® 



3.2.4 Synchronous Motor 




[MS 



3.2.5 Mechanically Coupled Machines 



o=o 



3.2.6 Induction Motor, Three-Phase, Squirrel Cage 



<& 



3.2.6.1 Induction motor with wound rotor 




3.2.7 Transformers with Two Separate Windings 




3.2.8 Auto-Transformer 







3.2.9 3-Phase Transformer with Three Separate 
Windings — Star — Star — Delta 




14 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



3.2.10 Starter 



3.2.19 Isolator 



3.2.11 Direct-on-Line Starter for Reversing Motor 



\ 




3.2.12 Star-Delta Starter 



a 



3.2.13 Auto -Transformer Starter 



3.2.14 Rheostatic Starter 




3.2.15 Switch 



3.2.16 Contactor 



i 
i 



3.2.17 Relay 



•tfSft**" 



3p 

W2I 



3.2.18 Circuit-Breaker 



o 



PART 1 GENERAL AND COMMON ASPECTS 



3.2.20 Earth Leakage Circuit Breaker 



A\ 



3.2.21 Residual Current Circuit Breaker 



h*- 



3.2.22 Surge Protective Device 



\-T7^H 



3.2.23 Fuse 



3.2.24 Signal Lamp 




3.2.25 Link 



3.2.26 Distribution Board, Cubicle Box, Main Fuse 
Board with Switches 



■ — i 



3.2.27 Socket Outlet, 5A 



Y°*A 



15 



SP 30: 2011 

Socket Outlet, ISA 



3.2.28 Plug 



3.2.29 Voltmeter 



3.2.30 Ammeter 



3.2.31 Wattmeter 



3.2.32 Varmeter 



i 

© 

© 
© 



3.2.33 Power Factor Meter 




3.2.34 Ohmmeter 



© 



3.2.35 Indicating Instrument (general symbol) 



o 



3.2.36 Recording Instrument (general symbol) 







3.2.37 Integrating Meter 










3.2.38 Watthour Meter 










Wh 



3.2.39 Clock 



© 



3.2.4© Master Clock 




3.2.41 Current Transformer 

3.2.42 Voltage Transformer 

Uu 

pn 

3.2.43 Wiring on the Surface 



3.2.44 Wiring in Conduit 



3.2.45 Lamp 



X 



16 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



3.2.46 Lamp Mounted on a Ceiling 

3.2.47 Emergency Lamp 



3.2.57 Aerial 



3.2.48 Spot Light 



(8= 



3.2.49 Flood Light 




3.2.50 Heater 

-am- 

3.2.51 Storage Type Water Heaters 

mm 

-US- 

3.2.52 5e// 

it 

3.2.53 Buzzer 



3.2.54 Ceiling Fan 



3.2.55 Exhaust Fan 



v 



oo 




3.2.56 Fan Regulator 



r\ 



Y 



3.2.58 Radio Receiving Set 



3.2.59 Television Receiving Set 



3.2.60 Manually Operated Fire Alarm 



3.2.61 Automatic Fire Detector Switch 



<* 



4 LETTER SYMBOLS AND SIGNS 

4.0 General 

4.0.1 Quantities and units used in electrotechnology 
cover in addition to electricity and magnetism other 
subjects such as radiation and light, geometry, 
kinematics, dynamics and thermodynamics. Several 
disciplines interact with the result that terminology used 
in one discipline becomes closely interrelated with that 
of the other. In order to enable uniform understanding 
of the meaning they represent, the letter symbols and 
signs used in abbreviations for denoting quantities, their 
functions and units shall conform to those recommended 
in IS 3722 (Part 1) and IS 3722 (Part 2). 

4.0.2 Guidance on the choice of alphabet and their type, 
representation of vector quantities, symbols of units, 
numerical values, and guidance on the use of subscripts 
are covered in IS 3722 (Part 1). 

Ready reference tables for symbols and subscripts are 
contained in IS 3722 (Part 2). For the purposes of this 
Code, a list of symbols, names of quantities and of 
constants and subscripts referred to frequently is given 
in 4.1. 

4.1 Symbols and Subscripts 

4.1.1 Table 1 of IS 3722 (Part 2) gives a reference list 
of symbols and subscripts used in electrotechnology. 



PART 1 GENERAL AND COMMON ASPECTS 



17 



SP 30: 2011 



ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS ON GRAPHICAL SYMBOLS 



IS No. 

2032 

(Part 15) : 1976 
(Part 19) : 1977 

(Part 25): 1980 
3722 

(Part 1) : 1983 

(Part 2) : 1983 

10381 : 1982 



11353: 1985 



12032 (Parti): 
1987/IEC 
60617-1 (1985) 

12032 (Part 2): 
1987/IEC 
60617-2 (1983) 



Title 

Graphical symbols used in electro- 
technology: 

Aircraft electrical symbols 
Electrical equipment used in 
medical practice 
Electrical installations in ships 
Letter symbols and signs used in 
electrical technology: 
General guidelines on symbols 
and subscripts 

Reference tables for symbols and 
subscripts 

Terms (and their Hindi 
equivalents) commonly used for 
name plates and similar data of 
electrical power equipment 
Guide for uniform system of 
marking and identification of 
conductors and apparatus terminals 
Graphical symbols for diagrams in 
the field of electrotechnology: 
Part 1 General information, general 
index, cross reference table 
Graphical symbols for diagrams in 
the field of electrotechnology: 
Part 2 Symbols elements, 
qualifying symbols and other 



IS No. 



12032 (Part 3) : 



12032 (Part 4): 

1987/IEC 

60617-4 (1984) 
12032 (Part 6): 

1987/IEC 

60617-6 (1983) 

12032 (Part 7): 
1987/IEC 
60617-7 (1983) 

12032 (Part 8): 
1987/IEC 
60617-8 (1983) 

12032 (Part 11): 
1987/IEC 
60617-11 (1983) 



Title 

symbols having general 

application 

Graphical symbols for diagrams 

in the field of electrotechnology: 

Part 3 Conductors and connecting 

devices 

Graphical symbols for diagrams in 

the field of electrotechnology: 

Part 4Passive components 

Graphical symbols for diagrams in 

the field of electrotechnology: 

Part 6 Production and conversion 

of electrical energy 

Graphical symbols for diagrams in 

the field of electrotechnology: 

Part 7 Switchgear, controlgear and 

protective 

Graphical symbols for diagrams in 

the field of electrotechnology: Part 8 

Measuring instruments, lamps 

and signalling devices 

Graphical symbols for diagrams in 

the field of electrotechnology: Part 

1 1 Architectural and topographical 

installation plans and diagrams 



18 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



SECTION 4 GUIDE FOR PREPARATION OF DIAGRAMS, 
CHARTS, TABLES AND MARKING 



FOREWORD 

Various types of diagrams and charts are required to be 
prepared during the planning and execution stages of 
an electrical installation work. It is therefore necessary 
to define the different types of diagrams, charts and 
tables, their purposes and format and the guiding 
principles for preparing them for the sake of uniformity. 

This Section 4 of the Code covers general guidelines 
on the subject. A list of relevant Indian Standards is 
given at Annex A. 

The guidelines for marking of conductors given in 3.6. 
Table 1 are in line with the guidelines accepted 
internationally on such matters. They provide for a 
common basis for understanding and identifying 
conductors and apparatus terminals, but more 
important, ensure safety to operating, maintenance 
personnel. 

1 SCOPE 

This Part 1 /Section 4 of the Code covers guidelines 
for preparation of diagrams, charts and tables in 
electrotechnology and for marking of conductors. 

2 REFERENCES 

A list of Indian Standards on general guidelines on various 
types of diagrams and charts is given at Annex A. 

3 PREPARATION OF DIAGRAMS, CHARTS 
AND TABLES 

3.0 General 

3.0.1 Diagram 

A diagram may show the manner in which the various 
parts of a network, installation, group of apparatus or items 
of an apparatus are interrelated and or interconnected. 

3.0.2 Chart 

A chart may show the interrelation between; 

a) different operations. 

b) operations and time. 

c) operations and physical quantities, and 

d) states of several items. 

3.0.3 Table 

A table replaces or supplements a diagram or a chart. 

3.1 Classification According to Purpose 
3.1.0 The main classifications are: 



a) Explanatory diagrams, 

b) Explanatory charts or tables, 

c) Wiring diagrams or wiring tables, and 

d) Location diagrams or tables. 

3.1.1 Explanatory Diagrams 

Explanatory diagrams are intended to facilitate the 
study and understanding of the functioning of an 
installation or equipment. Three types are defined 
below: 

a) Block diagram — Relatively simple diagram 
to facilitate the understanding of the principle 
of operation. It is a diagram in which an 
installation or equipment together with its 
functional interrelationships are represented 
by symbols, block symbols or pictures 
without necessarily showing all the 
connections. 

b) Circuit diagram — Explanatory diagram 
intended to facilitate the understanding of the 
functioning in detail. It shows by symbols an 
installation or part of an installation and the 
electrical connections and other links 
concerned with its operation. 

c) Equivalent circuit diagram — Special type 
of circuit diagram for the analysis and 
calculation of circuit characteristics. 

3.1.2 Explanatory Charts or Tables 

Explanatory charts or tables are intended to facilitate 
the study of diagrams and to give additional 
information. Two examples are given below: 

a) Sequence chart or table — gives the 
successive operation in a specified order, and 

b) Time sequence chart or table — is one which 
in addition takes account of the time intervals 
between successive operations. 

3.1.3 Wiring Diagrams or Wiring Tables 

Wiring diagrams are intended to guide the making and 
checking of the connection of an installation or 
equipment. For an equipment, they show the internal 
or external connections or both. The diagrams may 
sometimes show the layout of the different parts and 
accessories, such as terminal blocks and the wiring 
between them. 

3.1.3.1 Unit wiring diagram 

Diagram is representing all connections within a unit 
of an installation. 



PART 1 GENERAL AND COMMON ASPECTS 



19 



SP 30 : 2011 



3.1.3.2 Interconnection diagram 

Diagram representing the connections between the 
different units of an installation. 

3.1.3.3 Terminal diagram 

Diagram showing the terminals and the internal and/or 
external conductors connected to them. 

NOTE — Any of the wiring diagram may be replaced or 
supplemented by a table. 

3.1,4 Location Diagrams or Tables 

A location diagram or table contains detailed 
information about the location of parts of the 
equipment, for example, terminal blocks, plug-in units, 
sub-assemblies, modules, etc. It shows the item 
designations used in related diagrams and tables. 

NOTES 

1 A location diagram need not necessarily be to scale. 

2 Several types of diagrams may be combined into a single 
diagram, forming a mixed diagram. The same drawing may 
form both an explanatory and wiring diagram. 

3.2 Classification According to Method of 
Representation 

3.2,1 The method of representation is distinguished by: 

a) the number of conductors, devices or elements 
represented by a single symbol (see 3.2.1 J); 

b) the arrangement of the symbols representing 
the elements or parts of an item of apparatus 
(for example, detached or assembled) (see 
3.2.1); and 

c) the placing of the symbols to correspond with 
the topographical layout of the devices (see 
3.2.1.3). 

3.2.1.1 Number of conductors 

According to the number of conductors, devices or 
elements represented by a single symbol, the two 
methods of representation as given below may be 

distinguished. 

a) Single -line representation — Two or more 
conductors are represented by a single line. 

In particular, a single line may represent: 

1 ) circuits of a multi-phase system, 

2) circuits which have a similar electrical 
function, 

3) circuits or conductors which belong to 
the same signal path, 

4) circuits which follow the same physical 
route, and 

5) conductor symbols which would follow 
the same route on the diagram. 



Several similar items of apparatus may 
accordingly be represented by a single 
symbol, 
b) Multi-line representation — Each conductor 
is represented by an individual line. 

3.2.1.2 Arrangement of symbols 

According to the arrangement of the symbols 
representing the elements or parts of an item of 
apparatus on the diagram, the methods of 
representation are given below: 

a) Assembled representation — The symbols for 
the different parts of an item of apparatus or 
of an installation or equipment are drawn in 
close proximity on the diagram. 

b) Semi-assembled representation — The 
symbols for the different parts of an item of 
apparatus or of an installation are separated 
and arranged in such a way that the symbols 
for mechanical linkages between the parts 
which work together may be drawn easily. 

c) Detached representation — The symbols for 
the different parts of an item of apparatus or 
of an installation are separated and arranged 
in such a way that the circuits may easily be 
followed. 

3.2.1.3 Topographical representation 

The positions of the symbols on the diagram 
correspond wholly or partly to the topographical 
(physical) location of items represented. 

The following are examples where topographical 
representation may be used. 

a) Wiring diagrams, 

b) Architectural diagrams, and 

c) Network diagrams. 

NOTE — Several of these methods of representation may be 
used on the same diagram. 

3.3 Item Designation 

3.3.1 Item is a term used for component equipment, 
plant, unit, etc, which is represented by a graphical 
symbol on a diagram. The item designation is shown 
at an appropriate place near the graphical symbol of 
the item. This designation correlates the item on 
different diagrams, parts list, circuit descriptions and 
in the equipment. 

3.3.2 An item designation may be used for general or 
special purposes depending on the kind of information 
required. Guidelines on assignment of item 
designation, groups together with standard letter codes 
for the same are covered in IS 8270 (Part 2). 



20 



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SF 30 : 2011 



3.4 General Rules for Diagrams 

3.4.1 Paper sizes for drawings shall preferably be 
according to the international A-series (see IS 1064). 
The choice of drawing sizes should be decided after 
taking into account the necessary factors enumerated 
in 2.2 of IS 8270 (Part 2). 

3.4.2 In IS 2032, different kinds of symbols as well as 
symbols of different forms are shown. All the possible 
examples are also not covered there. Any symbol may 
be composed using the guidance from relevant Part of 
IS 2032 and Part 1/Section 3 of the Code. The basic 
rules for the choice of symbols shall be: 

a) to use the simplest form of symbol adequate 
for the particular purpose, 

b) to use a preferred form wherever possible, and 

c) to use the chosen form consistently 
throughout the same set of documentation. 

3.4.3 Specific guidelines on the application of IS 2032 
(All parts) from the point of view of choice of 
alternative symbols, symbol sizes, line thickness, 
orientation of symbols and methods of indicating 
symbol location are covered in IS 8270 (Part 3). 

3.5 Interconnection Diagrams and Tables 

3.5.1 Interconnection diagrams and tables provide 
information on the external electrical connections 
between equipment in an installation. They are used 
as an aid in the fabrication of wiring and for 
maintenance purposes. Information on the internal 
connections of units are normally not provided but 
references to the appropriate circuit diagram [see 
IS 8270 (Part 4)] may be provided. 

3.5.2 The diagrams may employ single or multiple 
representation and may be combined with or replaced 
by tables, provided clarity is maintained. Tables are 
recommended when the number of interconnections 
is large. 

3.5.3 Guidance on layout, identification and types of 
interconnection diagrams and tables are given in 
IS 8270 (Part 5). 

3.6 Marking and Arrangement of Conductors 

3.6.0 General 

3.6.0.1 The purpose of marking is to provide a means 
whereby conductors can be identified in a circuit and 
also after they have been detached from the terminals 
to which they are connected. Main marking is a system 
of marking characterizing each conductor or group of 



conductors irrespective of their electrical function. 
Supplementary marking is used as supplement to a 
main marking based on the electrical function of each 
conductor or group of conductors. 

3.6.0.2 The various methods of marking applicable to 
electrical installations and the equipment which form 
part of them are covered in IS 5578. 

3.6.1 Identification of Insulated and Bare Conductors 

For the purposes of this Code, the provisions of Table 1 
shall apply for the general application of marking 
conductors in installation. The rules also apply for 
marking conductors in assembles, equipment and 
apparatus. Reference is also drawn to the provision 
contained in relevant Indian Standard. 

3.6.2 Arrangement of Conductors 

3.6.2.0 Bus-bars and main connections which are 
substantially in one plane shall be arranged in the order 
given in either 3.6.2.1 or 3.6.2.2 according to the 
system. The relative order remains applicable even if 
any poles of the system are omitted. 

3.6.2.1 AC systems 

The order of phase connection shall be red, yellow and 
blue: 

a) When the run of the conductors is horizontal, 
the red shall be on the top or on the left or 
farthest away as viewed from the front. 

b) When the run of the conductors is vertical, 
the red shall be on the left or farthest away as 
viewed from the front. 

c) When the system has a neutral connection in 
the same place as the phase connections, the 
neutral shall occupy an outer position. 

d) Unless the neutral connection can be readily 
distinguished from the phase connections, the 
order shall be red, yellow, blue and black. 

3.6.2.2 DC systems 

The arrangement shall be as follows: 

a) When the run of the conductors is horizontal, 
the red shall be on the top or on the left or 
farthest away as viewed from the front. 

b) When the run of the conductors is vertical, 
the red shall be on the left or farthest away as 
viewed from the front. 

c) When the system is 3-wire with the 
conductors in the same place, the neutral shall 
occupy the middle position. 



PART 1 GENERAL AND COMMON ASPECTS 



21 



SP 30: 2011 



Table 1 Alphanumeric Notation, Graphical Symbols and Colours 

(Clause 3.6.1) 



SI No. 


Designation of Conductors 




Identification by 




''Alphanumeric 


Graphical 


Colour ^ 






Notation 


Symbol 




(1) 


(2) 


(3) 


(4) 


(5) 




Phase 1 


LI 




Red 


i) 


Supply ac system Phase 2 


L2 




Yellow 




Phase 3 


L3 




Blue 




Neutral 


N 




Black 




Phase 1 


U 




Red 




Phase 2 


V 




Yellow 


ii) 


Apparatus ac system phase 3 


w 




Blue 




Neutral 


N 




Black 




Positive 


L+ 


+ 


Red 


iii) 


Supply dc system Negative 


L- 


- 


Blue 




Midwire 


M 




Black 


iv) 


Phuse 
Supply dc system (single phase) NeutraJ 


L 

N 




Red 

Black 


v) 


Protective conductor 


PE 




Green and Yellow 


vi) 


Earth 


E 




No colour other than the colour of the 








bare conductor. If insulated, the 










colour for insulation so chosen to 










avoid those listed above for 










designation of other conductors 


vii) 


Noiseless (clean earth) 


TE 




Under consideration 


viii) 


Frame or chassis 


MM 




— 


ix) 


Equipotential Terminal 


CC 




— 



ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS ON DIAGRAMS, CHARTS, TABLES AND MARKING 



IS No. 


Title 


IS No. 




1064 : 1980 


Specification for paper standard 


8270 




2032 


sizes 

Graphical symbols used in 








electrotechnology : 


(Part 1) : 


: 1976 


(Part 15): 1976 


Aircraft electrical symbols 


(Part 2) : 


1976 


(Part 19) : 1977 


Electrical equipment used in 


(Part 3) : 


1977 




medical practice 


(Part 4) : 


: 1977 


(Part 25) : 1980 


Electrical installations in ships 


(Part 5) : 


: 1976 


5578 : 1984 


Guide for marking of insulated 








conductors 


(Part 6) : 


1983 



Title 

Guide for the preparation of 

diagrams, charts and tables for 

electrotechnology: 

Definitions and classification 

Item designation 

General requirements for diagrams 

Circuit diagram 

Interconnection diagrams and 

tables 

Unit wiring diagrams and tables 



22 



NATIONAL ELECTRICAL CODE 



SF 30: 2011 



SECTION 5 UNITS AND SYSTEMS OF MEASUREMENT 



FOREWORD 

The International System of Units (SI) have received 
worldwide acceptance and are accepted in most of the 
countries. It had been introduced in India under the 
Weights and Measures Act, 1976. Use of SI Units in 
matters relating to electrical engineering practice has 
many advantages. 

This Section 5 of the Code for reasons of brevity is 
restricted to electrical units only. 

1 SCOPE 

This Part 1 /Section 5 of the Code covers units and 
systems of measurement in electrotechnology. 

2 REFERENCE 

The following Indian Standard may be referred for 
further information: 

'IS 10005 : 1994/ISO 1000 : 1992 SI units and 
recommendations for the use of their multiples and of 
certain other units'. 

3 UNITS AND SYSTEMS OF MEASUREMENT 

3.1 Absolute Units 

3.1.1 Ampere (Unit of Electric Current) 

A constant current which, maintained in two parallel 
straight conductors of infinite length, of negligible 
circular cross-section an placed at a distance of one 
metre apart in a vacuum will produce a force of 
2 x 10~ 7 Newton per metre length between the 
conductors. 

3.1.2 Coulomb (Unit of Quantity of Electricity) 

The quantity of electricity conveyed in one second by 
a current of one ampere. 

3.1.3 Farad (Unit of Electric Capacitance) 

The capacitance of an electric capacitor having a 
difference of electric potential of one volt between the 



plates, when it is charged with a quantity of electricity 
of one coulomb. 

3.1.4 Henry (Unit of Electric Inductance) 

The inductance of a closed circuit in which an emf of 
one volt is produced when the current in the circuits 
varies at the uniform rate of one ampere per second. 

3.1.5 Ohm (Unit of Electrical Resistance) 

The electrical resistance between two points of a 
conductor when a constant potential difference of one 
volt, applied to these points, produces a current of one 
ampere in the conductor, provided no emf is generated 
in the conductor. 

3.1.6 Volt (Unit of Electric Potential Difference) 

The difference of electric potential which exists 
between two points of a conductor carrying a constant 
current of one ampere, when the power dissipated 
between these points is one watt. 

3.1.7 Weber (Unit of Magnetic Flux) 

The magnetic flux which, linked with a circuit 
composed of a single turn produces in it an emf of one 
volt if it is uniformly reduced to zero in one second. 

3.1.8 Watt (Unit of Electric Power) 

The power which results in the production of energy 
at the rate of 1 J/s. 

3.1.9 Siemens (Unit of Electric Conductance) 

The conductance of a conductor of resistance 1 ohm 
and is numerically equal to 1 ohm -1 . 

3.1.10 Tesla 

The tesla is a magnetic flux density of 1 Wb/m 2 . 

3.2 The electrical units defined in 3.1, together with 
their expression in terms of other units, 
recommendations on the selection of their multiples 
and submultiples and supplementary remarks (if any) 
are enumerated in Table 1 . 



PART 1 GENERAL AND COMMON ASPECTS 



23 



SP 30 : 2011 



Table 1 Electrical Units of Measurement 

(Clause 3.2) 



Si 

No. 
(1) 



Quantity 

(2) 



Name Symbol Expression in Terms Expression in Terms 

of Other Units of SI Base Units 

(3) (4) (5) (6) 



Selection of Multiples 

(7) 



i) 


Electric current 


ampere 


A 


— 


— 


kA, mA, juA, nA, pA 


ii) 


Power 


watt 


W 


J/s 


m 2 .kgs~ 3 


GW, MW, kW, mW, j/W 


iii) 


Quantity of electricity, 
electric charge 


coulomb 


C 


— 


s.A 


kC, juC, nC, pC 


iv) 


Electric potential, 
potential difference, 
electromotive force 


volt 


V 


W/A 


mlkgs^A- 1 


MV,kV,mV,^V 


v) 


Capacitance 


farad 


F 


C/V 


m 2, kg.s" 1 .A~ 1 


mF, jjF, nF, pF 


vi) 


Electrical resistance 


ohm 


n 


V/A 


m 2 kg.s- 1 .A- 2 


Ga,MQ.KQ,ma, ...vQ 


vii) 


Conductance 


Siemens 


s 


A/V 


m^kg-'.s" 1 


kS, mS, uS 


viii) 


Magnetic flux 


weber 


Wb 


V.s 


m^kg.s-lA" 1 


mWb 


ix) 


magnetic flux density 


tesla 


T 


Wb/m 2 


kg.s-'.A- 1 


mT, juT. nT 


x) 


Inductance 


henry 


H 


Wb/A 


m 2 kg.s- 2 .A- 2 


mH,juH,nH,/?H 


xi) 


Conductivity 


siemens/metre 


S/m 


— 


m'kg-'.S 1 , A 1 


MS/m, kS/m 


xii) 


Electric field strength 


volt/metre 


V/m 


— 


m.kg.s~ 1 .A~ l 


M V/m, kV/m or V/mra, V/m, 
raV/m, ju V/m 


xiii) 


Permeability 


henry/metre 


H/m 


— 


m.kg.s- 2 A- 2 


jt/H/m, nH/m 


xiv) 


Permittivity 


farad per metre 


F/m 


— 


m-^kg-'.s 4 ^ 2 


//F/m, nF/m, pF/m 


xv) 


Reluctance 


1 per henry 


H- 1 


— 


m^kg-'.slA 2 


— 


xvi) 


Resistivity 


ohm/metre 


Q.m 


— 


m^kg.s^.A -2 


G^m, MQ m, kQm, Clem, 
mOm, /iUm, nQm 



24 



NATIONAL ELECTRICAL CODE 



SF 30: 2011 



SECTION 6 STANDARD VALUES 



FOREWORD 

Standardization of basic parameters such as voltage, 
currents and frequency is one of the primary exercizes 
undertaken at the national level. This standardization 
helps in laying a sound foundation for further work 
relating to product or installation engineering. The 
values of voltages recommended as standard in this 
Section are based on the contents of IS 12360 : 1988 
'Voltage bands for electrical installations including 
preferred voltages and frequency'. 

This history of standardization of system voltages 
particularly those of systems operating below medium 
voltage levels is enumerated in IS 12360. Reference 
to Indian Electricity Rules may also be made. 

1 SCOPE 

This Part 1/Section 6 of the Code covers standard values 
of ac and dc distribution voltages, preferred values of 
current ratings and standard system frequency. 

2 REFERENCES 

This Part 1 /Section 6 of the Code may be read in 
conjunction with the following Indian Standards: 

IS No. Title 

1076 (Part 1) : 1985/ Preferred numbers: Part 1 Series 
ISO 3 : 1973 of preferred numbers 

12360 : 1988 Voltage bands for electrical 

installations including preferred 
voltages and frequency 

3 STANDARD VALUES OF VOLTAGES 

3.0 General 

3.0.1 For the sake of completeness, all the standard 
values of voltages given in IS 12360 relating to ac 
transmission and distribution systems are reproduced 
in this Section. However, it is noted that for most of the 
types of installations covered in subsequent parts of the 
Code, only the lower voltage values would be relevant. 

3.0.2 For medium and low voltage of distribution 
system, the original recommended standard values of 
nominal voltages were 230 V for single-phase 
and 230/400 V for three-phase system. However, 
during 1959, to align with IEC recommendations and 
in view of the economic advantages they offered, 
values of 240 V single-phase and 240/415 V three- 
phase had been adopted with a tolerance of ± 6 percent. 
However, in view of the latest international 
developments, it was decided to align Indian 
Standards nominal system voltages with IEC 



recommendations and accordingly revise the values 
of ac nominal system voltages from 240/415 to 
230/400 with the tolerance of ± 10 percent and it was 
also decided to effect the complete transition by 
31 December 2009, as given in IS 12360. IS 12360 
may be referred for the latest values. 

3.0.3 In the case of voltages above 1 kV, the importance 
of highest system voltage, which are generally 10 
percent above the corresponding nominal voltages 
given in 2.1.2.1 is recognized and product standards 
relate the voltage rating of equipment with respect to 
highest system voltages only. 

3.1 Standard Declared Voltage 

3.1.1 Single-phase, Two -Wire System 

The standard voltage shall be 240 V(see 3.0.2). 

3.1.2 Three-phase System 

3.1.2.1 The standard voltages for three-phase system 
shall be as under: 

415 V (see 3.0.2) (Voltage to neutral— 

240 V) (see 3.0.2) 



3.3 kV 


66 kV 


6.6 kV 


110 kV 


11 kV 


132 kV 


22 kV 


220 kV 


33 kV 


400 kV 



NOTES 

1 However, in view of the latest international developments, 
it was decided to align Indian Standards nominal system 
voltages with IEC recommendations and accordingly revise 
the values of a.c. nominal system voltages from 240/415 to 
230/400 with the tolerance of ± 10 percent and it was also 
decided to effect the complete transition by 31 December 2009, 
as given in IS 12360 

2 These voltages refer to the line-to-line voltage. 

3 1 10 kV is not a standard voltage for transmission purposes 
but this value has been included for the sake of equipment that 
are required for use on the 1 10 kV systems already in existence. 
It is realized that because of economic and other considerations, 
extensions to existing systems at this voltage may have to be 
made at the same voltage. 

3.1.3 The standard dc distribution voltage shall be 
220/440 V 

3.2 Voltage Limits for ac Systems 

3.2.1 The voltage at any point of the system under 
normal conditions shall not depart from the declared 
voltage by more than the values given below: 

a) 6 percent in the case of low or medium voltage 
(see 3.0.2); or 



PART 1 GENERAL AND COMMON ASPECTS 



25 



SP 30: 2011 



NOTE — Supply variation will become 230 V ± 10 percent 
with effect from 31 December 2009. See IS 12640 : 1988 for 
the latest provision. 

b) 6 percent on the higher side or 9 percent on 
the lower side in the case of high voltage; or 

c) 12.5 percent in the case of extra high voltage. 

NOTE — The permissible variations given above are in 
accordance with Indian Electricity Rules, 1956, and are 
applicable to the supply authorities. 

3.2.2 For installation design purposes, the limits of 
voltage between which the system and the equipment 
used in the system shall be capable of operating 
continuously are as follows: 



System Voltage 


Highest Voltage 


Lowest Voltage 


(U n ) 


(UJ 




(1) 


(2) 


(3) 


240 V 


264 V 


216 V 


415 V 


457 V 


374 V 


3.3 kV 


3.6 kV 


3.0 kV 


6.6 kV 


7.2 kV 


6.0 kV 


11 kV 


12 kV 


10 kV 


22 kV 


24 kV 


20 kV 


33 kV 


36 kV 


30 kV 


66 kV 


72.5 kV 


60 kV 



System Voltage 

(1) 



Highest Voltage 

(2) 



Lowest Voltage 
(3) 



132 kV 


145 kV 


120 kV 


220 kV 


245 kV 


200 kV 


400 kV 


420 kV 


380 kV 



NOTES 

1 This variation in voltage should not be confused with the 
permissible variation from the declared voltage as given 
in 3.2.1. 

2 For system voltage 230/400 highest voltage and lowest 
voltage shall be ±10 percent. 

4 PREFERRED CURRENT RATINGS 

4.1 The preferred current ratings shall be selected from 
the R5 series. If intermediate values are required, the 
same shall be selected from R10 series [see IS 1076 
(Part 1)]. 

5 STANDARD SYSTEM FREQUENCY 

5.1 The standard system frequency shall in 50 Hz. 

5.2 The limits within which the frequency is to be 
maintained are governed by the Indian Electricity 
Rules. 



26 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



SECTION 7 FUNDAMENTAL PRINCIPLES 



FOREWORD 

The basic criteria in the design of electrical 
installation are enumerated in this Section which 
could be taken note of in the planning stages. The 
specific nature of each occupancy calls for additional 
information which are summarized in the respective 
Sections of the Code. 

Assistance has been derived for this Section from IEC 
60364- 1 'Low- voltage electrical installations — Part 1 : 
Fundamental principles, assessment of general 
characteristics, definitions' issued by the International 
Electrotechnical Commission. Measures for achieving 
protection against the various hazards are under 
consideration by the National Electrical Code Sectional 
Committee. It may be added that subsequent 
requirements of the Code would, however, provide 
sufficient guidelines in respect of achieving the desired 
level of safety. 

1 SCOPE 

This Part 1 /Section 7 of the Code enumerates the 
fundamental principles of design and execution of 
electrical installations. 

2 REFERENCE 

Reference has been made to the following Indian 
Standard: 

IS No. Title 

IS 3792 : 1978 Guide for heat insulation of non- 

industrial buildings 

3 FUNDAMENTAL PRINCIPLES 

3.0 General 

3.0,1 Conformity with Indian Electricity Rules 

The installation shall generally be carried out in 
conformity with the requirements of the Indian 
Electricity Rules, 1956 as amended from time to time, 
and also the relevant regulations of the electric supply 
authority concerned. 

3.0.2 Materials 

All materials, fittings, equipment and their accessories, 
appliances, etc, used in an electrical installation shall 
conform to Indian Standards wherever they exist. In 
case an Indian Standard does not exist, the materials 
and other items shall be those approved by the 
competent authority. 



3.0.3 Workmanship 

Good workmanship is an essential requirement for 
compliance with this Code. Unless otherwise exempted 
under the Indian Electricity Rules, the work on 
electrical installations shall be carried out under the 
supervision of a person holding a certificate of 
competency issued by a recognized authority. The 
workmen shall also hold the appropriate certificate of 
competency. 

3.1 Coordination 

3.L1 Exchange of Information 

3.1.1.1 Proper coordination and collaboration between 
the architect, building engineer and the electrical 
engineer shall be ensured from the planning stage of 
the installation. The provisions that would have to be 
made for the accommodation of substation, transformer 
switchgear rooms, lift wells and other spaces required 
to be provided for service cable ducts, openings, etc. 
in the civil work, and such other relevant data shall be 
specified in advance. 

3.1.1.2 In all cases, that is, whether the proposed 
electrical work is a new installation or an extension to 
the existing one, or a modification, the relevant 
authority shall be consulted. In all such cases, it shall 
also be ensured that the current carrying capacity and 
the condition of the existing equipment and accessories 
are adequate. 

3.1.1.3 Sufficient coordination shall be ensured with 
the civil architect in the initial stages itself to ensure 
that sufficient building space be allotted for electrical 
installation purposes such as those required for sub- 
station installation, from the point of safety. 

3.1.1.4 The building services plan shall also include 
at the early stages all the details of services that 
utilize electrical energy and the requirements of the 
electrical installation in order to enable the designers 
and others involved to decide the coordination to 
be ensured. 

3.2 Distance from Electric Lines 

No building shall be allowed to be erected or re- 
erected, or any additions or alterations made to the 
existing building, unless the following minimum 
clearances are provided from the overhead electric 
supply lines: 



PART 1 GENERAL AND COMMON ASPECTS 



27 



SP 30: 2011 



SI 

No. 



Type of 

Supply 

Line 



(1) (2) 



Voltage 



(3) 



Clearance 



Vertical Hori- 
m zontal, m 

(4) (5) 



i) 



ii) 



Low and 
medium 
voltage 



High 
voltage 



Up to and 
including 
11000V 
Above 11 kVup 
to and including 
33 kV 



iii) Extra high 
voltage 



2.5. 



3.7 



3.7 



3.7 
(see 

Note) 



1.2 



1.2 



2.0 



■2.0 

(see 

Note) 



NOTE — For extra high voltage lines apart from the minimum 
clearances indicated, a vertical and horizontal clearance of 
0.30 m for every additional kV or part thereof shall be provided. 



3.3 Lighting and Ventilation 

From the point of view of conserving energy, it is 
essential to consider those aspects of design of 
buildings as vital, which would enable use of natural 
lighting and ventilation to the maximum. Attention is, 
however, drawn to the general requirements stipulated 
in Part 1/Section 14. 

3.4 Heat Insulation 

3.4.1 For information regarding recommended limits 
of thermal transmittance of roofs and walls and 
transmission losses due to different constructions, 
reference shall be made to IS 3792. 

3.4.2 Proper coordination shall be ensured to provide 
for necessary arrangements to install and serve the 
electrical equipment needed for the air-conditioning 
and heating services in the building. 

3.5 Lifts and Escalators 

For information of the electrical engineer, the lift/ 
escalator manufacturer in consultation with the building 
planners, shall advise of the electrical requirements 
necessary for the lifts and escalators to be installed in 
the building. General provisions are outlined in 
Part 1/Section 14. 

3.6 Location and Space for Electrical Equipment 

Even though specific provisions regarding the choice 
of location and space requirements for electrical 
installation in buildings have been provided in the 
relevant parts of the Code. The following aspects shall 
be taken note of in general while planning the building 
design: 



a) Need for and location and requirements of 
building substation. 

b) Load centre and centre of gravity of buildings, 

c) Layout, 

d) Room/spaces required for electrical utility, 

e) Location and requirements of switch rooms, 

f) Levels of illumination, and 

g) Ventilation. 

4 DESIGN OF ELECTRICAL INSTALLATION 

4.0 General 

4.0.1 The design of the electrical installation shall take 
into account the following factors: 

a) The protection of persons, livestock and 
property in accordance with 4.1, and 

b) The proper functioning of the electrical 
installation for the use intended. 

4.0.2 The following factors shall therefore be kept in 
view: 

a) Characteristics of the available supply or 
supplies, 

b) Nature of demand, 

c) Emergency supply or supplies, 

d) Environmental conditions, 

e) Cross-section of conductors, 

f) Type of wiring and methods of installations, 

g) Protective equipment, 
h) Emergency control, 

j) Disconnecting devices, and 
k) Preventing of mutual influence between 
electrical and non-electrical installations. 

4.1 Protection for Safety 

4.1.0 The requirements stated in 4.1.1 to 4.1.6 are 
intended to ensure the safety of persons, livestock and 
property against dangers and damage which may arise 
in the reasonable use of electrical installations. 

NOTE — In electrical installations, two major types of risks 
exist. 

a) Shock currents; and 

b) Excessive temperatures likely to cause burns, fires and other 
injurious effects. 

4.1.1 Protection Against Direct Contact 

Persons and livestock shall be protected against danger 
that may arise from contact with live parts of the 
installation. 

The protection can be achieved by one of the following 
methods: 

a) Preventing a current from passing through the 
body of any person or any livestock, and 



28 



NATIONAL ELECTRICAL CODE 



SP 30: -2011 



b) Limiting the current which can pass through 
a body to a value lower than the shock 
current. 

4.1.2 Protection Against Indirect Contact 

Persons and livestock shall be protected against dangers 
that may arise from contact with exposed conductive 
parts. 

This protection can be achieved by one of the following 
methods: 

a) Preventing a fault current from passing 
through the body of any person or any 
livestock. 

b) Limiting the fault current which can pass 
through a body to a value lower than the shock 
current. 

c) Automatic disconnection of the supply on the 
occurrence of a fault likely to cause a current 
to flow through a body in contact with 
exposed conductive parts, where the value of 
that current is equal to or greater than the 
shock current. 

4.1.3 Protection Against Thermal Effects in Normal 
Service 

The electrical installation shall be so arranged that there 
is no risk of ignition of flammable materials due to 
high temperature or electric arc. Also, during normal 
operation of the electrical equipment, there shall be 
no risk of persons or livestock suffering burns. 

4.1.4 Protection Against Overcurrent 

Persons or livestock shall be protected against injury, 
and property shall be protected against damage due to 
excessive temperatures or electromechanical stresses 
caused by any overcurrents likely to arise in live 
conductors. 

This protection can be achieved by one of the following 
methods: 

a) Automatic disconnection on the occurrence 
of an overcurrent before this overcurrent 
attains a dangerous value taking into account 
its duration, and 

b) Limiting the maximum overcurrent to safe 
value and duration. 

4.1.5 Protection Against Overvoltage 

Persons or livestock shall be protected against injury 
and property shall be protected against any harmful 
effects of a fault between live parts of circuits supplied 
at different voltages. 

Persons or livestock shall be protected against injury 
and property shall be protected against damage from 



any excessive voltages likely to arise due to other 
causes (for example, atmospheric phenomena or 
switching voltages). 

4.1.6 Methods for Protection for Safety 

While the general principles of protection against 
hazards in an electrical installation are given in 4.1.1 
to 4.1.6 guidelines on the methods for achieving 
protection and the choice of a particular protective 
measure are under consideration. 

4.2 Other Factors of Design 

4.2.1 Characteristics of the Available Supply or Supplies 

a) Nature of current: ac and/or dc, 

b) Nature and number of conductors: 

1) For ac: 

i) phase conductors(s), 
ii) neutral conductor, and 
iii) protective conductor. 

2) For dc: 

i) conductors equivalent to those listed 
above. 

c) Values and tolerances; 

1) voltage and voltage tolerances (see 
Part 1 /Section 6), 

2) frequency and frequency tolerances {see 
Part 1/Section 6), 

3) maximum current allowable, and 

4) prospective short-circuit current (see 
Part 1/Section 13). 

d) Protective measures inherent in the supply, 
for example, earthed (grounded) neutral or 
mid- wire. 

e) Particular requirements of the supply 
undertaking. 

4.2.2 Nature of Demand 

The number and type of the circuits required for 
lighting, heating, power, control, signalling, 
telecommunication, etc, are to be determined by: 

a) locations of points of power demand, 

b) loads to be expected on the various circuits, 

c) daily and yearly variation of demand, 

d) any special conditions, 

e) requirements for con trol, signaling, 
telecommunication, etc. 

4.2.3 Emergency Supply or Supplies (see also Part 2 
of the Code) 

a) Source of supply (nature, characteristics), and 

b) Circuits to be supplied by the emergency 
source. 



PART 1 GENERAL AND COMMON ASPECTS 



29 



SP 30: 2011 



4.2.4 Environmental Conditions ( see Part 1/Section 8) 

4.2.5 Cross-section of Conductors 

The cross- section of conductors shall be determined 
according to; 

a) their admissible maximum temperature, 

b) the admissible voltage drop, 

c) the electromechanical stresses likely to occur 
due to short-circuits, 

d) other mechanical stresses to which the 
conductors may be exposed, and 

e) the maximum impedance stresses to which the 
conductors of the short-circuit protection. 

4.2.6 Type of Wiring and Methods of Installations 

The choice of the type of wiring and the methods of 
installation depend on: 

a) nature of the location, 

b) nature of the walls or other parts of the 
building supporting the wire, 

c) accessibility of wiring to persons and livestock, 

d) voltage, 

e) electromechanical stresses likely to occur due 
to short-circuits, and 

f) other stresses to which the wiring may be 
exposed during the erection of the electrical 
installation or in service. 

4.2.7 Protective Equipment 

The characteristics of protective equipment shall be 
determined with respect to their function which may 
be, for example, protection against the effects of: 

a) overcurrent (overload, short-circuit) 

b) earth-fault current, 



c) overvoltage, and 

d) undervoltage and no- voltage. 

The protective devices shall operate at values of current, 
voltage and time which are suitably related to the 
characteristics of the circuits and to the possibilities of 
danger. 

4.2.8 Emergency Control 

Where in case of danger, there is necessity for 
immediate interruption of supply, in interrupting 
device shall be installed in such a way that it can be 
easily recognized and effectively and rapidly 
operated. 

4.2.9 Disconnecting Devices 

Disconnecting devices shall be provided so as to permit 
disconnection of the electrical installation, circuits or 
individual items of apparatus as required for 
maintenance, testing, fault detection or repair. 

4.2.10 Prevention of Mutual Influence Between 
Electrical and Non-electrical Installations 

The electrical installation shall be arranged in such a 
way that no mutual detrimental influence will occur 
between the electrical installation and non-electrical 
installations of the building. 

4.2.11 Accessibility of Electrical Equipment 

The electrical equipment shall be arranged so as to 
afford as may be necessary: 

a) sufficient space for the initial installation and 
later replacement of individual items of 
electrical equipment, and 

b) accessibility for operation, testing, inspection, 
maintenance and repair. 



30 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



SECTION 8- ASSESSMENT OF GENERAL CHARACTERISTICS 

OF BUILDINGS 



FOREWORD 

An assessment of the general characteristics of 
buildings is essential before planning for the needs 
of an electrical installation. This Part 1 /Section 8 
covers a checklist of various factors that require 
assessment. 

This Part 1 /Section 8 follows the internationally 
recommended method of identification of the external 
influences on the electrical installation such as 
environment, utilization and method of construction of 
the building. Out of these influences, those which are 
specifically important for specific occupancies are listed 
at the relevant Sections of the Code. However, it is hoped 
that this Section 8 would also enable understanding of 
installations not explicitly covered by the Code. 

The contents of this Part 1 /Section 8 are primarily 
intended for installations inside buildings though to 
the extent possible they could be utilized for outdoor 
sites. However more severe conditions may prevail 
at outdoor sites and these require special 
considerations. 

1 SCOPE 

This Part 1 /Section 8 of the Code covers guidelines 
for assessing the characteristics of buildings and the 
electrical installation therein. 

2 ASSESSMENTOFGENERALOH^yt4CIERISTICS 
OF BUILDINGS 

An assessment of the general characteristics of 
buildings as enumerated below is essential from the 
point of view of design and protection for safety of the 
electrical installation. These characteristics when 
assessed shall also be taken into consideration in the 
selection and erection of equipment. 

2.1 Identification of General Characteristics 
2.1.1 Purposes, Supplies and Structure 
The following shall be assessed; 

a) Maximum demand and diversity from the 
point of view of economic and reliable design 
{see 3.2.2 of Part 1/Section 7). 

b) Type of distribution system, which includes, 
types of systems of live conductors and types 
of system earthing. 

NOTE — For types of system earthing, see Part 1/ 
Section 14. 



c) Supply characteristics such as nature of 
current, nominal voltage, prospective short- 
circuit currents. 

NOTE — This assessment shall include those 
characteristics of main, standby and safety supply 
services. 

d) Division of installation from the point of view 
of control, safe operation, testing and 
maintenance. 

2.2 Identification of External Influences on the 
Electrical Installation 

2.2.1 The characteristics of the following external 
influences shall be assessed: 

a) Environments 



1) 


Ambient temperature, 


2) 


Atmospheric humidity, 


3) 


Altitude, 


4) 


Presence of water, 


5) 


Presence of foreign solid bodies, 


6) 


Presence of corrosive or polluting 




substances, 


7) 


Mechanical stresses, 


8) 


Presence of flora and/or mould growth, 


9) 


Presence of fauna, 


10) Electromagnetic, electrostatic or ionizing 




influences, 


11) Solar radiation, 


12) Seismic effects, 


13) Lighting, and 


14) 


Wind. 


Utilization 


1) 


Capability of persons, 


2) 


Electrical resistance of human body, 


3) 


Contact of persons with earth potential, 


4) 


Conditions of evacuation in an 



emergency, and 
5) Nature of processed or stored material. 
c) Construction of Buildings 

1) Constructional materials, and 

2) Building design. 

2.2.2 Table 1 suggests the classification and 
codification of external influences which require 
assessment in the design and erection of electrical 
installation. 



PART 1 GENERAL AND COMMON ASPECTS 



31 



SP 30 : 2011 



Table 1 Assessment of General Characteristics of Buildings 

(Clause 2.2.2) 



si 

No. 

(1) 



Class Designation 

(2) 



Characteristics 

(3) 



Application and Examples Code 

(4) (5) 



i) Environment 

1) Ambient 
temperature 



The ambient temperature to be considered for 
the equipment is the temperature at the place 
where the equipment is to the installed 
resulting from the influence of all other 
equipment in the same location, when 
operating, not taking into account the thermal 
contribution of the equipment to be installed. 
Lower and upper limits of range of ambient 
temperature: 





Lower Limits 


Upper Limits 


a) 


-60°C 


+5°C 


b) 


-40°C 


+5°C 


c) 


-25°C 


+5°C 


d) 


-5°C 


+40°C 


e) 


+5°C 


+40°C 


f> 


-5°C 


+60°C 



2) Atmospheric humidity 

3) Altitude 

4) Presence of water: 
a) Negligible 



The average temperature over a 24 hour period 
must not exceed 5°C below the upper limits. 
Combination of two ranges to define some 
environments may be necessary. Installation 
subject to temperatures outside the ranges 
require special consideration. 
Under consideration 

< 2 000 m 
> 2 000 m 

Probability of presence of water is negligible 



b) Free-falling drops Possibility of vertically falling drops 



c) Sprays 

d) Splashes 

e) Jets 

f) Waves 

g) Immersion 

h) Submersion 



5) Presence of foreign 
solid bodies: 

a) Negligible 

b) Small objects 

c) Very small objects 



Possibility of water falling as spray at an 
angle up to 60°C from the vertical 
Possibility of splashes from any direction 



Possibility of jets of water from any direction 

Possibility of water waves 

Possibility of intermittent partial or total 
covering by water 



Possibility of permanent and total covering by 
water 



The quantity of nature of dust or foreign solid 
bodies is not significant 
Presence of foreign solid bodies where the 
smallest dimension is not less than 2.5 mm 
Presence of foreign solid bodies where the 
smallest dimension is not less than 1 mm 



Locations in which the walls do not 
generally show traces of water but may do so 
for short periods, for example, in the form of 
vapour which good ventilation dries rapidly 
Locations in which water vapour 
occasionally condenses as drops or where 
steam may occasionally be present 
Locations in which sprayed water forms a 
continuous film on floors and/or walls 
Locations where equipment may be 
subjected to splashed water, this applies, for 
example, to certain external lighting fittings, 
construction site equipment, etc 
Locations where hosewater is used regularly 
(yards, car-washing bays) 
Seashore locations such as piers, beaches 
quays, etc 

Locations which may be flooded and or 
where water may be at least 150 mm above 
the highest point of equipment, the lowest 
part of equipment being not more than 1 m 
below the water surface 
Locations such as swimming pools where 
electrical equipment is permanently and 
totally covered with water under a pressure 
greater than 0. 1 bar 



Tools and small objects of which the smallest 
dimension is at least 2.5 mm 
Wires are examples of foreign solid bodies 
of which the smallest dimension is not less 
than 1 mm 



AA1 
AA2 
AA3 
AA4 
AA5 
AA6 



AC1 

AC2 

AD1 



AD2 

AD3 
AD4 

ADS 
AD6 

AD7 

AD8 



AE1 
AE2 
AE3 



32 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



Table 1 — (Continued) 



SI 


Class Designation 


Characteristics 


(1) 


(2) 


(3) 



Application and Examples Code 

(4) (5) 



d) Dust 
6) Presence of corrosive 
or polluting substances: 

a) Negligible 

b) Atmospheric 



c) Intermittent or 
accidental 



d) Continuous 

7) Mechanical stresses: 

a) Impact 

Low severity 
Medium severity 
High severity 



b) Vibration 
Low severity 
Medium severity 
High severity 



c) Other mechanical 
stresses 
8) Presence of fungus 
and/or mould growth: 

a) No hazard 

b) Hazard 



9) Presence of vermin: 

a) No hazard 

b) Hazard 



NOTE — In conditions AE1 and AE3, dust 
may be present but is not significant to 
operation of the electrical equipment 
Presence of dust in significant quantity 



The quantity or nature of corrosive or 
polluting substances is not significant 
The presence of corrosive or polluting 
substance of atmospheric origin is significant 



Intermittent or accidental subjection to 
corrosive or polluting chemical substances 
being used or produced 



Continuously subject to corrosive or polluting 
chemical substances in substantial quantity 



Installation situated by the sea or industrial 
zones producing serious atmospheric 
pollution, such as chemical works and 
cement works; this type of pollution arises 
especially in the production of abrasive, 
insulating or conductive dusts 
Location where some chemical products are 
handled in small quantities and where these 
products may come only accidentally into 
contact with electrical equipment; such 
conditions are found in factory, laboratories, 
other laboratories or in locations where 
hydro-carbons are used (boiler-rooms, 
garages, etc) 
For example, chemical works 



Household and similar conditions 
Usual industrial conditions 
Severe industrial conditions 



NOTE — Provisional classification. 
Quantitative expression of impact severities is 
under consideration. 



NOTE — Provisional classification. 
Quantitative expression of vibration severities 
is under consideration. 



No hazard of fungus and/or mould growth 
hazard of fungus and/or mould growth 



No hazard 

Hazard from fauna (insects, birds, small 

animals) 



Household and similar conditions where the 

effects of vibration are generally negligible 

Usual industrial conditions 

Industrial installations subject to severe 

conditions 



Under consideration 



The hazard depends on local conditions and 
the nature of fungus. Distinction should the 
made between harmful growth of vegetation 
or conditions for promotion of mould growth 



The hazard depends on the nature of the 
vermin. Distinction should be made 
between: 

a) presence of insects in harmful quantity or 

of an aggressive nature. 

b) presence of small animals or birds in 

harmful quantity or of an aggressive 
nature 



AE4 

AF1 

AF2 



AF3 



AF4 



AG1 
AG2 
AG3 



AH1 
AH2 
AH3 



AJ 



AK1 
AK2 



AL1 
AL2 



10) Electro magnetic, 

electrostatic or ionizing 
influences: 



PART 1 GENERAL AND COMMON ASPECTS 



33 



SP 30: 2011 



Table 1 — (Continued) 



SI Class Designation 

No. 

(1) (2) 



Characteristics 



(3) 



Application and Examples Code 

(4) (5) 



a) Negligible 



b) Stray currents 

c) Electromagnetics 

d) Ionization 

e) Electrostatics 

f) Induction 

11) Solar radiation: 

a) Negligible 

b) Significant 

12) Seismic effects: 

a) Negligible 

b) Low severity 

c) Medium severity 

d) High severity 



13) Lightning: 

a) Negligible 

b) Indirect exposure 

c) Direct exposure 



14) Wind 

(Under consideration) 

ii) Utilization 
1 ) Capability of persons: 

a) Ordinary 

b) Children 



c) Handicapped 

d) Instructed 

e) Skilled 



No harmful effects from stay currents, 
electromagnetic radiation, electrostatic fields, 
ionizing radiation or induction 
Harmful hazards of stray currents 
Harmful presence of electromagnetic radiation 
Harmful presence of ionizing radiation 
Harmful presence of electrostatic fields 
Harmful presence of induced currents 



Solar radiation of harmful intensity and/or 
duration 

Up to 30 gal (1 gal=lcm/s 2 ) 
Over 30 up to and including 300 gal 
Over 300 up to and including 600 gal 
Greater than 600 gal 



Hazard from supply arrangements 
Hazard from exposure of equipment 



2) Electrical resistance of 
the human body 
classification 

(Under consideration) 

3) Contact of persons with 
earth potential: 

a) None 

b) Low 



c) Frequent 

d) Continuous 



Uninstructed persons 

Children in locations intended for their 

occupation. 

NOTE — This class does not necessarily apply to 

family dwellings 

Persons not in command of all their physical and 

intellectual abilities (sick persons, old persons) 

Persons adequately advised or supervised by 

skilled persons to enable them to avoid 

dangers which electricity may create 

(operating and maintenance staff) 

Persons with technical knowledge or 

sufficient experience to enable them to avoid 

dangers which electricity may create 

(engineers and technicians) 



Persons in non-conducting situations 
Persons do not in usual conditions make 
contact with extraneous conductive parts or 
stand on conducting surfaces 
Persons are frequently in touch with 
extraneous conductive parts or stand on 
conducting surfaces 
Persons are in permanent contact with 
metallic surroundings and for whom the 
possibility of interrupting contact is limited 



Vibration which may cause the destruction 
of the building is outside the classification. 
Frequency is not taken into account in the 
classification; however, if the seismic wave 
resonates with the building, seismic effects must 
be specially considered. In general, the frequency 
of seismic acceleration is between and 10 Hz 



Installations supplied by overhead lines. 
Part of installations located outside 
buildings. The risks AQ2 and AQ3 relate to 
regions with a particularly high level of 
thunderstorm activity 



AMI 



AM2 
AM3 
AM4 
AM5 
AM6 

AN1 
AN2 



API 
AP2 
AP3 

AP4 



AQ1 
AQ2 
AQ3 



Nurseries 

Hospitals 

Electrical operating areas 

Closed electrical operating areas 



Non-conducting locations 



Locations with extraneous conductive parts, 
either numerous or of large area 

Metallic surroundings such as boilers and 
tanks 



BA1 
BA2 



BA3 
BA4 



BA5 



BB 



BC1 
BC2 



BC3 



BC4 



34 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



Table 1 — (Concluded) 



SI 

No. 


Class Designation 


Characteristics 


Application and Examples 


Code 


(1) 


(2) 


(3) 


(4) 


(5) 



4) Conditions of 
evacuation in an 
emergency 



Low density occupation, easy conditions of 

evacuation 

Low density occupation, difficult conditions 

of evacuation 

High density occupation, easy conditions of 

evacuation 

High density occupation, difficult conditions 

of evacuation 



5) Nature of processed or 
stored materials 

a) No significant risks 

b) Fire risks 

c) Explosion risk 



d) Contamination 
risks 



iii) Constructions of 
Building 

1) Constructional 
materials: 

a) Non-combustible 

b) Combustible 

2) Building Design: 

a) Negligible risk 

b) Propagation of fire 



c) Movement 



d) Flexible or unstable 



Manufacture, processing or storage of 
flammable materials including presence of dust 
Processing or storage of explosive or low 
flashpoint materials including presence of 
explosive dusts 

Presence of unprotected foodstuffs, pharma- 
ceutics, and similar products without protection 



Buildings mainly constructed of 
combustible materials 



Buildings of which the shape and 

dimensions facilitate the spread of fire (for 

example, chimney effects) 

Risks due to structural movement (for 

example, displacement between a building 

and the ground, or settlement of ground or 

building foundations) 

Structures which are weak or subjects to 

movement (for example, oscillation) 



Buildings of normal or low height used for 

habitation 

High-rise buildings 

Locations open to the public (theatres, 

cinemas) 

High-rise buildings open to the public (hotels, 

hospitals, etc) 



Barns, wood-working shops, paper factories 
Oil refineries, hydrocarbon stores 

Foodstuff industries, kitchen 

NOTE — Certain precautions may be necessary in 
the event of fault, to prevent processed materials 
being contaminated by electrical equipment, for 
example, by broken lamps 



Wooden buildings 



High-rise buildings, Forced ventilation 
systems 

Buildings of considerable length or erected on 

unstable ground. 

Contraction or expansion joints 

Tents, air-support structures, false ceilings, 

removable partitions 

Flexible wiring, Installations needing support 



BD1 
BD2 
BD3 
BD4 



BE1 
BE2 

BE3 



CM 
CA2 



CB1 
CB2 



CB3 



CB4 



NOTES 

1 Each condition of external influence is designated by a code comprising a group of two capital letters and a number as follows: 

The first letter relates to the general category of external influence 

A = environment 

B = utilization 

C = construction of buildings 

The second letter relates to the nature of the external influence 

A,., 

B ... 

C... 

The number relates to the class within each external influence 

1 ... 
2... 
3... 

For example, the code AC2 signifies: 

A = environment 

AC = environment altitude, and 

AC2 = environment altitude > 2 000 m. 

The Code given here is not intended to be used for marking equipment. 

2 The characteristics defined for electrical installations are those accepted by the IEC and as applicable for electrical installations in 
buildings. Influences on outdoor installations are separately defined in the respective parts of the Code. 



PART 1 GENERAL AND COMMON ASPECTS 



35 



SP 30: 2011 



For the time being, the characteristics of influences 
(Table 1 , col 3) are given in descriptive language only. 
Codification for the same {see Note 1), as 
recommended by IEC are given at Table 1 col 5 for 
information. 

2.3 Compatibility 

An assessment shall be made of any characteristics of 
equipment likely to have harmful effects upon other 
electrical equipment or other services or likely to impair 
the supply. Those characteristics include, for example: 

a) Transient overvoltages, 

b) Rapidly fluctuating loads, 

c) Starting currents, 

d) Harmonic currents, 

e) dc feedback, 

f) High-frequency oscillations, and 

g) Earth leakage currents . 



2.4 Maintainability 

An assessment shall be made of the frequency and 
quality of maintenance the installation can reasonably 
be expected to receive during its intended life. Where 
an authority is to be responsible for the operation of 
the installation, that authority shall be consulted. Those 
characteristics are to be taken into account in applying 
the requirements of this Code so that, having regard to 
the frequency and quality of maintenance expected, 

a) Any periodic inspection and testing and 
maintenance and repairs likely to be necessary 
during the intended life can be readily and 
safely carried out, 

b) Effectiveness of the protective measures for 
safety during the intended life is ensued, and 

c) Reliability of equipment for proper 
functioning of the installation is appropriate 
to the intended life. 



36 



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SP 30: 2011 



SECTION 9 WIRING INSTALLATIONS 



FOREWORD 

A major portion of fixed installation design in a 
building relates to wiring installation. This Section of 
the Code is primarily intended to cover guidelines on 
design and construction of wiring installations which 
are commonly applicable to all types of occupancies. 
The requirements specified in this Section are based 
on safety and reliability considerations. 

The general design guidelines for wiring given in this 
Section have to be carefully considered while applying 
them to specific occupancies and a proper selection of 
the method is to be decided depending on local 
conditions. Guidance on such matters is covered in 
respective Sections of the Code. 

Assistance for this Section has been derived from 
IEC 60364-5-52 (20001) 'Electrical installations 
of buildings — Part 5-52: Selection and erection of 
electrical equipment — Wiring systems'. 

1 SCOPE 

This Section 9 of the Code covers the essential design 
and constructional requirements for electrical wiring 

installations. 

2 REFERENCES 

A list of relevant Indian Standards on electrical wiring 
is given at Annex A. 

3 TERMINOLOGY 

For the purpose of this Part 1 /Section 9, the definitions 
given in Part 1/Section 2 of this Code and the following 
shall apply. 

3.1 Cabfie Ducting System — A system of closed 
enclosure of non-circular sections for insulated 
conductors, cable and cords in electrical installations, 
allowing them to be drawn in and replaced. 

3.2 Conduit Fitting — A device designed to join or 
terminate one or more components of a conduit system, 
or change direction. 

3.3 Conduit Joint — An interface between two or more 
components of a conduit system, or between a conduit 
system and other equipment. 

3.4 Cable Trunking System — A system of closed 
enclosures comprising a base with a removable cover 
intended for the complete surrounding of insulated 
conductors, cables, cords and/or for the 
accommodation of other electrical equipment. 



3.5 Conduit System — A closed wiring system 
consisting of conduits and conduit fittings for the 
protection and management of insulated conductors 
and/or cables in electrical or communication 
installations, allowing them to be drawn in and/or 
replaced, but not inserted laterally. 

NOTE — Within the conduit system there shall be no sharp 
edges, burrs or surface projections which are likely to 
damage insulated conductors or cables or inflict injury to 
the installer or user. The manufacturer shall be responsible 
for providing guidelines to assist the safe installation of the 
conduit system. 

3.6 Distribution Board — A unit comprising one or 
more protective devices against over current and 
ensuring the distribution of electrical energy to the 
circuits. 

3.7 Luminaire — Apparatus which distributes, filters 
or transforms the light transmitted from one or more 
lamps and which includes all the parts necessary for 
supporting, fixing and protecting the lamps, but not 
the lamps themselves, and where necessary circuit 
auxiliaries together with the means for connecting them 
to the supply. 

4 GENERAL AND COMMON ASPECTS FOR 
SELECTION OF WIRING SYSTEMS 

4.1 Cable and Conductors for Low/Medium Voltage 

Every non-flexible cable cord for use at low/medium 
voltage, busbar trunking system, and every conductor 
other than a cable for use as an overhead line operating 
at low medium voltage shall comply with the 
appropriate Indian Standards. 

Flexible cable or flexible cord shall be used for fixed 
wiring only where the relevant provisions of this Code 
are met. 

4.1.1 Cable for ac Circuits — Electromagnetic Effects 

Single-core cables armoured with steel wire or tape 
shall not be used for ac circuits. Conductors of ac 
circuits installed in ferromagnetic enclosure shall be 
arranged so that the conductors of all phases and the 
neutral conductor (if any) and the appropriate 
protective conductor of each circuit are contained in 
the same enclosure. 

Where such conductors enter a ferrous enclosure they 
shall be arranged so that the conductors are not 
individually surrounded by a ferrous material, or other 
provision shall be made to prevent eddy (induced) 
currents. 



PART 1 GENERAL AND COMMON ASPECTS 



37 



SF 30 : 2011 



4.1.2 Electromechanical Stresses 

Every conductor or cable shall have adequate strength 
and be so installed as to withstand the 
electromechanical forces that may be caused by any 
current, including fault current it may have to carry in 
service. 

4.2 Conduits and Conduit Fittings 

A conduit or conduit fitting shall comply with the 
appropriate Indian Standard. 

4.3 Trunking, Ducting and Fittings 

Where applicable, trunking, ducting and their fittings 
shall comply with IS 14927. Where IS 14927 does not 
apply, non-metallic trunking, ducting and their fittings 
shall be of insulating material complying with the 
ignitability characteristic 'P' of relevant Indian 
Standard. 

4.4 Lighting Track Systems 

A lighting track system shall comply with relevant 
Indian Standard 

4.5 Methods of Installation of Cables and 
Conductors 

The methods of installation of a wiring system for 
which the Code specifically provides are at 6. Other 
methods can be used provided that compliance with 
the Code is maintained. 

A bare live conductor shall be installed on insulators. 
Non-sheathed cables for fixed wiring shall be enclosed 
in conduit, ducting or trunking. Where cables having 
different temperature ratings are installed in the same 
enclosure, all the cables shall be deemed to have the 
lowest temperature ratings. 

4.6 Selection and Erection in Relation to External 
Influences 

Table 1 of Part 1/Section 8 contains a concise list of 
external influences which need to be taken into account 
in the selection and erection of wiring systems. 

4.6.1 Ambient Temperature (AA) 

A wiring system shall be selected and erected so as to 
be suitable for the highest and lowest local ambient 
temperature likely to be encountered. The components 
of a wiring system, including cables and wiring 
enclosures shall be installed or handled only at 
temperatures within the limits stated in the relevant 
product specification or as recommended by the 
manufacturer. 

4.6.2 External Heat Sources 

To avoid the effects of heat from external sources one 



or more of the following methods, or an equally 
effective method, shall be used to-protect the wiring 
system: 

a) shielding. 

b) placing sufficiently far from the source of 
heat. 

c) selecting a system with due regard for the 
additional temperature rise which may occur. 

d) reducing the current-carrying capacity. 

e) local reinforcement or substitution of 
insulating material. 

NOTE — Heat from external sources may be radiated, 
convected or conducted, for example 

a) from hot water systems, 

b) from plant appliances and luminaires, 

c) from manufacturing process, 

e) through heat conducting materials, 

f) from solar gain of the wiring system or its surrounding 
medium. 

Parts of a cable or flexible cord within an accessory, 
appliance or luminaire shall be suitable for the 
temperatures likely to be encountered, or shall be provided 
with additional insulation suitable for those temperatures. 

4.6.3 Presence of Water (AD) or High Humidity (AB) 

A wiring system shall be selected and erected so that 
no damage is caused by high humidity or ingress of 
water during installation, use and maintenance. Where 
water may collect or condensation may form in a wiring 
system provision shall be made for its harmless escape 
through suitably located drainage points. Where a 
wiring system may be subjected to waves (AD6), 
protection against mechanical damage shall be afforded 
by one or more of the methods given in 4,6.6 to 4.6.8. 

4.6.4 Presence of Solid Foreign Bodies (AE) 

A wiring system shall be selected and erected to 
minimize the ingress of solid foreign bodies during 
installation, use and maintenance. In a location where 
dust or other substance in significant quantity may be 
present (AE4: Light dust, AE5: Moderate dust or AE6: 
Heavy Dust) additional precautions shall be taken to 
prevent its accumulation in quantities which could 
adversely affect the heat dissipation from the wiring 
system. 

4.6.5 Presence of Corrosive or Polluting Substances 

(AF) 

Where the presence of corrosive or polluting substances 
is likely to give rise to corrosion or deterioration, parts 
of the wiring system likely to be affected shall be 
suitably protected or manufactured from materials 
resistant to such substances. Metals liable to initiate 
electrolytic action shall not be placed in contact with 



38 



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each other. Materials liable to cause mutual or 
individual deterioration or hazardous degradation shall 
not be placed in contact with each other. 

4.6.6 Impact (AG) 

A wiring system shall be selected and erected so as to 
minimize mechanical damage. In a fixed installation 
where an impact of medium severity (AG2) or high 
severity (AG3) can occur, protection shall be afforded 
by: 

a) the mechanical characteristics of the wiring 
system, or 

b) the location selected, or 

c) the provision of additional local or general 
mechanical protection, 

or by any combination of the above. 

Except where installed in a conduit or duct which 
provides equivalent mechanical protection, a cable 
buried in the ground shall be of a construction 
incorporating an armour or metal sheath or both, or be 
of insulated concentric construction. Such cable shall 
be marked by cable covers or a suitable marking tape 
or by suitable identification of the conduit or duct and 
be buried at a sufficient depth to avoid being damaged 
by any disturbance of the ground reasonably likely to 
occur. 

A wiring system buried in a floor shall be sufficiently 
protected to prevent damage caused by the intended 
use of the floor. 

Where a cable is installed under a floor or above a 
ceiling it shall be run in such a position that it is not 
liable to be damaged by contact with the floor or the 
ceiling or their fixings. Where a cable passes through 
a timber joist within a floor or ceiling construction or 
through a ceiling support ( for example, under 
floorboards), the cable shall be at least 50 mm measured 
vertically from the top, or bottom as appropriate, of 
the joist or batten. Alternatively, cable shall incorporate 
an earthed metallic sheath suitable for use as a 
protective conductor or shall be protected by enclosure 
in earthed steel conduit securely supported, or by 
equivalent mechanical protection sufficient to prevent 
penetration of the cable by nails, screws, and the like. 

Where a cable is to be concealed within a wall or 
partition at a depth of less than 50 mm from the surface 
its method of erection shall be that the cable shall be 
installed within 150 mm of the top of the wall or 
partition within 150 mm of an angle formed by two 
adjoining walls or partitions. Where the cable is 
connected to a point or accessory on the wall or 
partition, the cable may be installed outside these zones 
only in straight runs, either horizontally or vertically, 
to the point or accessory or switch gear. 



Where compliance as above is impracticable, the 
concealed cable shall incorporate an earthed metallic 
covering which complies with the requirements of this 
Code for a protective conductor of the circuit 
concerned, or shall be enclosed in earthed conduit, 
trunking or ducting satisfying the requirements of this 
Code for a protective conductor, or by mechanical 
protection sufficient to prevent penetration of the cable 
by nails, screws and the like. 

4.6.7 Vibration (AH) 

A wiring system supported by, or fixed to, a structure 
or equipment subject to vibration of medium severity 
(AH2) or high severity (AH3) shall be suitable for the 
conditions and in particular shall employ cable with 
fixings and connections suitable for such a situation. 

4.6.8 Other Mechanical Stresses (AJ) 

A wiring system shall be selected and erected so as to 
minimize during installation, use and maintenance, 
damage to the sheath and insulation of cables and 
insulated conductors and their terminations. 

Where the wiring system is designed to be 
withdrawable there shall be adequate means of access 
for drawing cable in or out and, if buried in the 
structure, a conduit or cable ducting system for each 
circuit shall be completely erected before cable is 
drawn in. The radius of every bend in a wiring system 
shall be such that conductors and cables shall not suffer 
damage. Where a conductor or a cable is not 
continuously supported it shall be supported by suitable 
means at appropriate intervals in such a manner that 
the conductor or cable does not suffer damage by its 
own weight. Every cable or conductor used as fixed 
wiring shall be supported in such a way that it is not 
exposed to undue mechanical strain and so that there 
is no appreciable mechanical strain on the terminations 
of the conductors, account being taken of mechanical 
strain imposed by the supported weight of the cable or 
conductor itself. A flexible wiring system shall be 
installed so that excessive tensile and torsional stresses 
to the conductors and connections are avoided. 

4.6.9 Presence of Flora and/or Mould Growth (AK) 

Where expected conditions constitute a hazard (AK2), 
the wiring system shall be selected accordingly or 
special protective measures shall be adopted. 

4.6.10 Presence of Fauna (AL) 

Where expected conditions constitute a hazard (AL2), 
the wiring system shall be selected accordingly or 
special protective measures shall be adopted. 

4.6.11 Solar Radiation (AN) 

Where significant solar radiation (AN2) is experienced 



PART 1 GENERAL AND COMMON ASPECTS 



39 



SP 30 : 2011 



or expected, a wiring system suitable for the conditions 
shall be selected and erected or adequate shielding shall 
be provided. 

4.6.12 Building Design (CB) 

Where structural movement (CB3) is experienced or 
expected, the cable support and protection system 
employed shall be capable of permitting relative 
movement so that conductors are not subjected to 
excessive mechanical stress. 

For flexible or unstable structures (CB4) flexible wiring 
systems shall be used. 

4.7 Current — Carrying Capacity of Conductors 

The current to be carried by any conductor for sustained 
periods during normal operation shall be such that the 
appropriate temperature limit specified is not exceeded. 
See various parts of IS 3961 for details. 

4.8 Voltage Drop in Consumer's Installations 

Under normal service conditions the voltage at the 
terminals of any fixed current-using equipment shall 
be greater than the lower limit corresponding to the 
Indian Standard relevant to the equipment wherever 
existing. In the absence of such a standard, then the 
Voltage at the terminals shall be such as not to impair 
the safe functioning of the equipment. 

The voltage drop between the origin of the installation 
(usually the supply terminal) and the fixed current- 
using equipment should not exceed 4 percent of the 



normal voltage of the supply. 

A greater voltage drop maybe accepted for a motor 
during starting periods and for other equipment with 
high inrush currents provided it is verified that the 
voltage variations are within the limits specified in the 
relevant Indian Standards for the equipment or, in the 
absence of a Indian Standard, in accordance with the 
manufacturer's recommendations. Temporary 
conditions such as voltage transients and voltage 
variation due to abnormal operation may be 
disregarded. 

4.9 Cross-sectional Areas of Conductors 

4.9.1 Phase Conductors in ac Circuits and Live 
Conductors in dc Circuits 

The nominal cross-sectional area of phase conductors 
in ac circuits and of live conductors in dc circuits shall 
be not less than the values specified in Table 1. 

4.10 Neutral Conductors 

For a polyphase circuit in which imbalance may occur 
in normal service, through significant inequality of 
loading or of power factor in the various phases, or 
through the presence of significant harmonic currents 
in the various phases, the neutral conductor shall have 
a cross-sectional area adequate to afford compliance 
with permissible conductor operating temperature for 
the maximum current likely to flow in it. 

For a polyphase circuit in which serious imbalance is 
unlikely to occur in normal service, other than a 



Table 1 Minimum Nominal Cross-sectional Area of Conductor 

{Clause 4.9.1) 



SI 

No. 



(1) 



Type of Wiring System 



(2) 



Use of the Circuit 



(3) 





Conductor 




-«**_ 






Material 


Minimum permissible nominal 




cross-sectional area 




mm 2 


(4) 


(5) 


Cu 


1.5 


J~Cu 

Lai 


2.5 


10 (see Note 1) 


Cu 


0.5 (see Note 2) 


Cu 


10 


Al 


16 


Cu 


4 


Cu 


As specified in the relevant 




Indian Standard 




0.5 {see Note 2) 




0.5 



Cables and insulated conductors f Lighting circuits 
) Power Circuits 



ii) Bare conductors 



iii) 



L Signalling and control circuits 
[Power circuits 



Is, 



Flexible connections with 
insulated conductors and cables 



gnalling and control circuits 
For a specific appliance 

For any other application 

Extra low voltage circuits for special 

applications 

NOTES 

1 Connectors used to terminate aluminium conductors shall be tested and approved for this specific use. 

2 In multicore flexible cables containing 7 or more cores and in signalling control circuits intended for electronic equipment a 
minimum nominal cross-sectional area of 0. 1 mm is permitted. 



40 



NATIONAL ELECTRICAL CODE 



SP 30: -2011 



discharge lighting current, multi-core cables 
incorporating a reduced neutral conductor in 
accordance with the appropriate Indian Standard may 
be used. Where single — core cables are used in such 
circuits, the neutral conductor shall have a 
cross-sectional area appropriate to the expected value 
of the neutral current. 

In a discharge lighting circuit the neutral conductor 
shall have a cross- sectional area not less than that of 
the phase conductor(s). 

4.11 Electrical Connections 

4.11.1 Connections Between Conductors and Between 
a Conductor and Equipment 

Every connection between conductors and between a 
conductor and equipment shall provide durable 
electrical continuity and adequate mechanical strength 
{see 4.6.8). 

4.11.2 Selection of Means of Connection 

The selection of the means of connection shall take 
account, as appropriate, of the following: 

a) material of the conductor and its insulation. 

b) number and shape of the wires forming the 
conductor. 

c) cross- sectional area of the conductor. 

d) number of conductors to be connected 
together. 

e) temperature attained by the terminals in 
normal service such that the effectiveness of 
the insulation of the conductors connected to 
them is not impaired. 

f) where a soldered connection is used the design 
shall take account of creep, mechanical stress 
and temperature rise under fault current 
conditions. 

g) provision of adequate locking arrangements 
in situations subject to vibration or thermal 
cycling. 

'4.11.3 Enclosed Connections 

Where a connection is made in an enclosure. The 
enclosure shall provide adequate mechanical protection 
and protection against relevant external influences. 
Every termination and joint in a live conductor or a 
PEN conductor shall be made within one of the 
following or a combination thereof: 

a) a suitable accessory complying with the 
appropriate Indian Standard. 

b) an equipment enclosure, complying with the 
appropriate Indian Standard. 

c) a suitable enclosure of material complying 



with the relevant glow wire test requirements 
of IS 11000 (Part 2/Secl). 

d) an enclosure formed or completed with 
building material considered to be non- 
combustible when tested appropriate Indian 
Standard relating to IS 3808. 

e) an enclosure formed or completed by part of 
the building structure, having the ignitability 
characteristic 'P' as specified in appropriate 
Indian Standard. 

Cores of sheathed cables from which the sheath has 
been removed and non-sheathed cables at the 
termination of conduit, ducting or trunking shall be 
enclosed as per specified enclosure at (b) above. 

4.11.4 Accessibility of Connections 

Except for the following, every connection and joint 
shall be accessible for inspection, test and maintenance: 

a) a compound-filled or encapsulated joint. 

b) a connection between a cold tail and a heating 
element (for example, a ceiling and floor 
heating system, a pipe trace-heating system). 

c) a joint made by welding, soldering, brazing 
or compression tool. 

4.12 Selection and Erection to Minimize the Spread 

of Fire 

4. 12. 1 Risk of Spread of Fire 

The risk of spread of fire shall be minimized by 
selection of an appropriate material and erection in 
accordance with this Code. The wiring system shall 
be installed so that the general building structural 
performance and fire safety are not materially reduced. 
A part of a wiring system which complies with the 
requirements of the relevant Indian Standard, which 
standard has no requirement for testing for resistance 
to the propagation of flame, shall be completely 
enclosed in non-combustible building material having 
the ignitability characteristic "P". 

Where a wiring system passes through elements of 
building construction such as floors, walls, roofs, 
ceilings, partitions or cavity barriers, the openings 
remaining after passage of the wiring system shall be 
sealed according to the degree of fire resistance 
required of the element concerned (if any). 

Where a wiring system such as conduit, cable ducting, 
cable trunking, busbar or busbar trunking penetrates 
elements of building construction having specified fire 
resistance it shall be internally sealed so as to maintain 
the degree of fire resistance of the respective element 
as well as being externally sealed to maintain the 
required fire resistance. A non-flame propagating 



PART 1 GENERAL AND COMMON ASPECTS 



41 



SP 30: 2011 



wiring system having a maximum internal 
cross-section of 710 mm 2 need not be internally sealed. 

Except for fire resistance over one hour, this 
requirement is satisfied if the sealing of the wiring 
system concerned has been type tested by the method 
specified in relevant Indian Standard. 

Each sealing arrangement used as above shall comply 
with the following requirements: 

a) It shall be compatible with the material of the 
wiring system with which it is in contact, and 

b) It shall permit thermal movement of the 
wiring system without reduction of the sealing 
quality, 

c) It shall be removable without damage to 
existing cable where space permits future 
extension to be made, and 

d) It shall resist relevant external influences to 
the same degree as the wiring system with 
which it is used. 

4.12.2 Erection Conditions 

During the erection of a wiring system temporary 
sealing arrangements shall be provided as appropriate. 
During alteration work sealing which has been 
disturbed shall be reinstated as soon as practicable. 

4.12.3 Verification 

Each sealing arrangement shall be visually inspected 
at an appropriate time during erection to verify that it 
conforms to the manufacturer's erection instructions 
and the details shall be recorded. 

4.13 Proximity to Other Services 

4.13.1 Proximity to Electrical Services 

4.13.1.1 Neither an extra-low voltage nor a low voltage 
circuit shall be contained within the same wiring system 
as a circuit of nominal voltage exceeding that of low 
voltage unless every cable is insulated for the highest 
voltage present or one of the following methods is 
adopted: 

a) each conductor in a multicore cable is 
insulated for the highest voltage present in 
the cable, or is enclosed within an earthed 
metallic screen of current-carrying capacity 
equivalent to that of the largest conductor 
enclosed within the screen, or 

b) the cables are insulated for the irrespective 
system voltages and installed in a separate 
compartment of a cable ducting or cable 
trunking system, or have an earthed metallic 
covering. 



4.13.1.2 A low voltage circuit shall be separated from 
an extra-low voltage circuit. 

4.13.1.3 Where an installation comprises circuits for 
telecommunication, fire-alarm or emergency lighting 
systems as well as circuits operating at low voltage 
and connected directly to a mains supply system, 
appropriate precautions shall be taken to prevent 
electrical contact between the cables of the various 
types of circuit. 

4.13.1.4 Fire alarm and emergency lighting circuits 
shall be segregated from all other cables and from each 
other. 

4.13.1.5 Where a common conduit, trunking, duct or 
ducting is used to contain cables of category 1 and 
category 2 circuits, all cables of category 1 circuits 
shall be effectively partitioned from the cables of 
category 2 circuits, or alternatively the latter cables 
shall be insulated in accordance with the requirements 
of the clauses for the highest voltage present in the 
category 1 circuits {see also 4.13.1.8). 

4.13.1.6 Where a category 3 circuit is installed in a 
channel or trunking containing a circuit of any other 
category, the circuits shall be segregated by a 
continuous partition such that the specified integrity 
of the category 3 circuit is not reduced. Partitions shall 
also be provided at any common outlets in a trunking 
system accommodating a category 3 circuit and a 
circuit of another category. Where mineral-insulated 
cable, or cable whose performance complies with 
appropriate Indian Standard relating to specification 
for performance requirements for cables required to 
maintain circuit integrity under fire conditions, is used 
for the category 3 circuit such a partition is not normally 
required. 

4.13.1.7 In conduit, duct, ducting or trunking systems, 
where controls or outlets for category 1 and category 2 
circuits are mounted in or on a common box, 
switchplate or block, the cables and connections of the 
two categories, of circuit shall be segregated by a 
partition which, if of metal, shall be earthed. . 

4.13.1.8 Where cores of a category 1 and a category 2 
circuit are contained in a common multicore cable, 
flexible cable or flexible cord, the cores of the category 
2 circuit shall be insulated individually or collectively 
as a group, in accordance with the requirements of this 
Code, for the highest voltage present in the category 1 
circuit, or alternatively shall be separated from the cores 
of the category 1 circuit by an earthed metal screen of 
equivalent current-carrying capacity to that of the cores 
of the category 1 circuit. Where terminations of the 
two categories of circuit are mounted in or on a 



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common box, switchplate, or block, they shall be 
segregated in accordance with 4.13.1.7. 

4.13.2 Proximity to Non-electrical Services 

4.13.2.1 Where a wiring system is located in close 
proximity to a non-electrical service both the following 
conditions shall be met: 

a) the wiring system shall be suitably protected 
against the hazards likely to arise from the 
presence of the other service in normal use, and 

b) protection against indirect contact shall be 
afforded in accordance with Part 1 /Section 7 
of this Code. 

4.13.2.2 A wiring system shall not be installed in the 
vicinity of a service which produces heat, smoke or 
fume likely to be detrimental to the wiring, unless 
protected from harmful effects by shielding arranged 
so as not to affect the dissipation of heat from the wiring. 

4.13.2.3 Where a wiring system is routed near a service 
liable to cause condensation (such as water, steam or 
gas services ) precautions shall be taken to protect the 
wiring system from deleterious effects. 

4.13.2.4 Where a wiring system is to be installed in 
proximity to a non-electrical service it shall be so 
arranged that any foreseeable operation carried out on 
either service will not cause damage to the other. 

4.13.2.5 Any metal sheath or armour of a cable 
operating at low voltage, or metal conduit, duct, ducting 
and trunking or bare protective conductor associated 
with the cable which might make contact with fixed 
metalwork of other services shall be either segregated 
from it, or bonded to it. 

4.13.2.6 No cable shall be run in a lift (or hoist) shaft 
unless it forms part of the lift installation as defined in 
the appropriate Indian Standard relating to Lifts and 
Service Lifts. 

4.14 Selection and Erection in Relation to 
Maintainability, Including Cleaning 

Where any protective measure must be removed in 
order to carry out maintenance, reinstatement of the 
protective measure shall be practicable without 
reducing the original degree of protection. Provision 
shall be made for safe and adequate access to all parts 
of the wiring system which may require maintenance. 

5 MAINS INTAKE AND DISTRIBUTION OF 
ELECTRICAL ENERGY IN. CONSUMERS' 

PREMISES 

5.1 Distribution Board System 

Distribution board system, also known as 'Distribution 
Fuse Board System' or 'Distribution Miniature Circuit 



Breaker (MCB) Board System' is most commonly 
adopted for distribution of electrical energy in a 
building. Appropriate protection shall be provided at 
distribution boards and at all levels of panels and 
switchboards for all circuits and sub-circuits against 
short circuit, over-current and other parameters as 
required. The protective device shall be capable of 
interrupting maximum prospective short circuit current 
that may occur, without danger. The ratings and settings 
of fuses and the protective devices shall be co-ordinated 
so as to afford selectivity in operation. Where circuit- 
breakers are used for protection of a main circuit and 
of the sub-circuits derived there from, discrimination 
in operation may be achieved by adjusting the 
protective devices of the sub-main circuit breakers to 
operate at lower current settings and shorter time-lag 
than the main circuit-breaker. It is recommended to 
provide residual current device (RCD) of 300/500 mA 
rating as part of the main board at the entry of the 
building and of 30 mA rating as part of the sub- 
distribution board. 

Where high rupturing capacity (HRC) type fuses are 
used for back-up protection of circuit breakers, or 
where HRC fuses are used for protection of main 
circuits, and circuit-breakers for the protection of sub- 
circuits derived therefrom, in the event of short-circuits 
protection exceeding the short-circuits protection 
exceeding the short-circuits capacity of the circuit 
breakers, the HRC fuses shall operate earlier than the 
circuit-breakers; but for smaller overloads within the 
short-circuit capacity of the circuit-breakers, the circuit- 
breakers shall operate earlier than the HRC fuse blows. 
If rewireable type fuses are used to protect sub-circuits 
derived from a main circuit protected by HRC type 
fuses, the main circuit fuse shall normally blow in the 
event of a short-circuit or earth fault occurring on sub- 
circuit, although discrimination may be achieved in 
respect of overload currents. The use of rewireable 
fuses is restricted to the circuits with short-circuit level 
of 4 kA; for higher level either cartridge or high 
rupturing capacity (HRC) fuses shall be used. 

A fuse carrier shall not be fitted with a fuse element 
larger than that for which the carrier is designed. The 
current rating of a fuse shall not exceed the current 
rating of the smallest cable in the circuit protected by 
the fuse. Every fuse shall have its own case or cover 
for the protection of the circuit and an indelible 
indication of its appropriate current rating in an 
adjacent conspicuous position. 

In Fig. 1, the two copper strips (busbars) fixed in a 
distribution board of hard wood or metal or other non- 
metal insulating case are connected to the "supply 
mains" through a linked switch with fuse or linked 
circuit breaker on each live conductor, so that the 
installation can be switched off as whole from both 



PART 1 GENERAL AND COMMON ASPECTS 



43 



SP 30: 2011 



DISTRIBUTION 
BOARD 




CIRCUIT N0.2 



Fig. 1 A Typical Distribution Board System 



poles of the supply, if required. A fuse or MCB is 
inserted in the phase pole of each circuit, so that each 
circuit is connected up through its own particular fuse 
or MCB. The lamps, fans, socket outlets for other 
domestic appliances consisting each circuit need not 
necessarily be in the same room or even on the same 
floor in case of a small building and simply allocated 
to each circuit in such a way that the raceways or runs 
for connecting them is most convenient and 
economical. The distribution board has 4 ways for four 
circuits but the number of ways and the circuits can be 
more, provided the cable feeding the board is large 
enough to carry the total load current. 

The practice in residential and similar commercial 
buildings is to restrict the maximum number of points 
of lights, fans and socket outlets in a final circuit. In 
order to ensure safety, in case more points are required 
to be connected to the supply, then it is to be done by 
having more than one final circuits. 

5.1.1 Main and Branch Distribution Board Systems 

5.1.1.1 The rating or setting of over-current protection 
devices shall be so chosen as to be suitable for 
protection of cables and conductors used in the circuit. 
Main distribution board shall be provided with a circuit- 
breaker on each pole of each circuit, or a switch with a 
fuse on the phase or live conductor and a link on the 
neutral or earthed conductor of each circuit. The 
switches shall always be linked. Main and branch 
distribution boards shall be provided, along with surge 
protective device and earth leakage protective device 
(incoming), with a fuse or a miniature circuit breaker 
or both of adequate rating/setting on the live conductor 
of each sub-circuit and the earthed neutral conductor 



shall be connected to a common link and be capable 
of being disconnected individually for testing purposes. 
At least one spare circuit of the same capacity shall be 
provided on each branch distribution board. Further, 
the individual branching circuits (outgoing) shall be 
protected against overcurrent with miniature circuit 
breaker of adequate rating. In residential/industrial 
lighting installations, the various circuits shall be 
separated and each circuit shall be individually 
protected so that in the event of fault, only the particular 
circuit gets disconnected. 

5.1.1.2 Functionally the residential installation wiring 
shall be separate for ceiling and higher levels in walls, 
portable or stationery plug in equipments. For devices 
consuming high power and which are to be supplied 
through supply cord and plug, separate wiring shall be 
done. For plug-in equipment provisions shall be made 
for providing ELCB protection in the sub-distribution 
board. It is preferable to have additional circuit for 
kitchen and bathrooms. Such sub-circuit shall not have 
more than a total of ten points of light, fans and 6 A 
socket outlets. The load of such circuit shall be 
restricted to 800 W. If a separate fan circuit is provided, 
the number of fans in the circuit shall not exceed ten. 
Power sub-circuit shall be designed according to the 
load but in no case shall there be more than two 16A 
outlets on each sub-circuit. The circuits for lighting of 
common area shall be separate. For large halls 3 -wire 
control with individual control and master control shall 
be made for effective conservation of energy. 

5.1.1.3 In industrial and other similar installations 
requiring the use of group control for switching 
operation circuits for socket outlets may be kept 
separate from fans and lights. Normally, fans and lights 



44 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



may be wired on a common circuit, however, if need 
is felt separate circuits may be provided for the two. 
The load on any low voltage sub-circuit shall not exceed 
3 000 W. In a case of new installation, all circuits and 
sub-circuits shall be designed by making a provision 
of 20 percent increase in load due to any future 
modification. Power sub-circuits shall be designed 
according to the load but in no case shall there be more 
than four outlets on each sub-circuit. In industrial 
installations the branch distribution board shall be 
totally segregated for single-phase distribution and 
wiring. 

5.1.1.4 In wiring installations at special places like 
construction sites, stadium, shipyards, open yards in 
industrial plants, etc, where a large number of high 
wattage lamp may be required, there shall be no 
restriction of load on any circuit but conductors used 
in such circuits shall be of adequate size for the load 
and proper circuit protection shall be provided. 

5.1.1.5 In large buildings, however, if only one 
distribution board were used, some of the points would 
be at a considerable distance from it and in such cases 
it is advisable to employ sub-distribution boards 
(known as final circuit distribution boards) known as 
branch distribution boards either to save cable or to 
prevent too great voltage drop at the more distant points 
(lamps, fans or other appliances). In such cases, the 
main distribution board controls the distribution circuits 
to each sub-distribution board from which the final 
circuits to loads are taken as shown in Fig. 2. 

5.1.1.6 The number of, 

a) sub-main circuits (also called distribution 
circuits) from main distribution board to sub- 
distribution boards. 



b) sub-distribution boards, also called branch 
distribution boards or final circuit distribution 
boards. 

c) final circuits to loads, are decided as per the 
number of points to be wires and load to be 
connected per circuit and total load to be 
connected to the supply system. 

5.1.1.7 For determination of load of an installation, 
the following ratings may be assumed, unless the values 
are known or specified: 



Connected Device 



Rating for Calculating 
Connected Load 



Fluorescent lamp 
Incandescent lamp, fan 
6A socket outlet 



16A socket outlet 



Exhaust fans, fluorescent 
lamps other than single 
lamp, compact fluorescent 
lamps, HVMV lamps, 
HVSV lamps 



40 W 

60 W 

100 W unless the actual 

value of loads are 

specified 

1000 W unless the 

actual value of loads are 

specified 

according to their 

capacity, control gear 

losses shall be also 

considered as applicable 



5.2 Distribution Boards 

Distribution boards which provide plenty of wiring 
space having terminals of adequate size to 
accommodate the cables which will be connected to 
them should be selected. Very often it is necessary to 
install a cable which is larger than would normally be 
required, in order to limit voltage drop, and take 




sua MAIN 

--, DISTRIBUTION 

t BOARD /NO.A 

I 

4-, 



SUB-CIRCUIT 
N0.2 
i M 1-2 L3 



C-L 



It »-3 






SUB-CIRCUIT N0.1 



Fig. 2 Typical House- wiring Circuit 



PART 1 GENERAL AND COMMON ASPECTS 



45 



SP 30 : 2011 



account of the presence of harmonics, variation of 
voltage; and sometimes the main terminals are not of 
sufficient size to accommodate these larger cables. 
Therefore distribution boards should be selected with 
main terminals of sufficient size for these larger cables. 

5.2.1 Branch Distribution Boards 

Branch distribution boards shall be provided, along 
with surge protective device and earth leakage 
protective devices (incoming), with a fuse or a 
miniature circuit breaker or both of adequate rating / 
setting chosen in accordance with IS 732 on the live 
conductor of each sub-circuit and the earthed neutral 
conductor shall be connected to a common link and be 
capable being disconnected individually for testing 
purposes. At least one spare circuit of the same capacity 
shall be provided on each branch distribution board. 
Further the individual branching circuits (outgoing) 
shall be protected against over current with miniature 
circuit-breaker of adequate rating. In residential / 
industrial lighting installation, the various circuits shall 
be separated and each circuit shall be individually 
protected so that in the event of fault, only the particular 
circuit gets disconnected. 

There are three types of distribution boards, 



a) those fitted with rewirable fuse links; 

b) those fitted with HBC fuse links; and 

c) those fitted with circuit-breakers. 

Refer to Fig. 3 for the above mantioned protective 
devices. 

There are several reservations to the use of rewirable 
fuses. It is difficult to prevent the replacement of 
rewirable fuse link by a larger size fuse link than the 
fuse link chosen at the time of the installation. If the 
fuse links are not of appropriate size to match the 
current carrying capacity of the installed circuit, it 
would lead to short-circuit and earth fault. 

Distribution boards can be fitted with MCBs or HBC 
fuse links. Distribution boards fitted with miniature 
circuit-breakers are more expensive in their first cost, 
but they have an advantage that they can incorporate 
an earth leakage trip. Miniature circuit-breakers are 
obtainable in ratings from 6 A to 63 A, all of which are 
of the same physical size, and are therefore easily 
interchangeable. However, they must not be 
interchanged without first making sure that are of the 
correct rating for the circuits they protect. Another 
advantage of using MCBs is that they can easily be 
reset after operation. 




FUSE BASE 



HEAT-RESISTANT 
PADDING 



FUSE ELEMENT 




3A Semi-enclosed Rewirable Fuses 
PORCELAIN BODY DETECTOR STRIP CONNECTION LUG 



QUARTZ FILLING 




7^ 

FUSE. ELEMENT 



METAL CAP 



3B High Breaking Capacity (HBC) Fuse 
Fig. 3 Protective Devices {Continued) 



46 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 




3C High Breaking Capacity (HBC) Fuse 




3D Miniature Circuit Breaker 
Fig. 3 Protective Devices 



5.2.2 Installation of Distribution Boards 

5.2.2.1 The distribution boards shall be located as near 
as possible to the centre of the load they are intended 
to control. The location should be convenient and 
economical for installation and use. Where two and/or 
more distribution fuse-boards feeding low voltage 
circuits are fed from a supply of medium voltage, these 
distribution boards shall be: 

a) arranged so that it is not possible to open two 
at a time, namely, they are interlocked and 
the metal case is marked 'Danger 415 Volts' 
and identified with proper phase marking and 
danger marks; or 

b) installed in a room or enclosure accessible to 
only authorized persons. 

5.2.2.2 In wiring branch distribution board, total load 
of consuming devices shall be divided as far as possible 
evenly between the number of ways in the board 
leaving spare circuits for future extension. All low 
voltage distribution boards shall be marked 'Lighting' 
or 'Power' or 'Lighting and Power', as the case may 
be, and also marked with the voltage and number of 
phases of the supply. Each shall be provided with a 
circuit list giving diagram of each circuit which it 



controls and the current rating of the circuit and size 
of fuse element. If a distribution board is recessed into 
a wall which is constructed of combustible materials 
such as wood, the case must be of metal or other non- 
combustible material. 

5.2.2.3 Distribution boards shall be of either metal- 
clad type, or air insulated type. But, if exposed to 
weather or damp situations, these shall be of the 
weatherproof type and, if installed where exposed to 
explosive dust, vapour or gas, these shall be of 
flameproof type in accordance with IS 5571. In 
corrosive atmospheres, these shall be treated with anti- 
corrosive preservative or covered with suitable plastic 
compound. 

5.2.3 Wiring of Distribution Boards 

5.2.3.1 The wiring shall be done on a distribution 
system through main and/or branch distribution boards. 
Main distribution board shall be controlled by a linked 
circuit-breaker or linked switch with fuse. Each 
outgoing distribution circuit or sub-main circuit from 
main distribution board to sub-distribution boards shall 
be provided with linked disconnector switch or linked 
MCB. Each outgoing final circuit from a main 
distribution board or branch distribution board shall 



PART 1 GENERAL AND COMMON ASPECTS 



47 



SP 30 : 2011 



be controlled by a miniature circuit-breaker (MCB) or 
a fuse on the phase or line conductor as in the case of 
single phase neutral (SPN) distribution board or three 
phase neutral distribution board. The branch 
distribution board shall be controlled by a linked 
switchfuse or linked circuit-breaker. Each outgoing 
circuit shall be provided with a fuse or miniature circuit 
breaker (MCB) of specified rating on the phase or live 
conductor. 

5.2.3.2 Three pole neutral (TPN) distribution boards 
are not generally recommended to be used for single 
phase 2 wire final circuit distribution. However, the 
use of TPN fuse distribution boards or TPN MCB 
distribution boards for single phase 2 wire final circuit 
distribution have come to practice and the same is 
permissible, provided the size of the neutral conductor 
wire is carefully designed, taking the unbalanced load 
condition, harmonic generation of loads etc. 

5.2.3.3 The neutral conductors (incoming and 
outgoing) shall be connected to a common link (multi- 
way connector) in the distribution board, and be 
capable of being disconnected individually for testing 
purposes. The wiring throughout the installation shall 
be such that there is no break in the neutral wire except 
in the form of a linked switchgear. 

5.2.3.4 There shall be at least two ring circuits — one 
for light current (known as light power) 6A socket 
outlets and another for heavy current (known as heavy 
power) 16A socket outlets to connect heavy current 
domestic appliances. Similarly, heavy current wiring 
shall be kept separate and distinct from "light current" 
wiring, from the level of circuits, that is, beyond the 
branch distribution boards. Lights, fans and call bells 
shall be wired in the light current circuits. 

5.2.3.5 Wiring shall be separate or essential loads, that 
is, those fed through standby supply and non essential 
loads throughout. Wiring for the safety services shall 
be separate and distinct. Unless and otherwise 
specified, wiring shall be done only by the "Looping 
System". Phase or live conductors shall be looped at 
the switch boxes and neutral conductors at the point 
outlets. Where "joint box system" is specified for 
installation, all joints in the conductors shall be made 
by means of approved mechanical connector in suitable 
and approved junction boxes. 

5.2.3.6 The balancing of circuits in three wire or poly 
phase installations shall be arranged before hand. 

5.2.4 Location of Distribution Boards 

5.2.4.1 Distribution boards should preferably be sited 
as near as possible to the centre of the loads they are 
intended to control. This will minimize the length and 
cost of final circuit cables, but this must be balanced 
against the cost of submain cables. Best location of 



distribution boards depends on the availability of 
suitable stanchions or walls, the case with which circuit 
wiring can be run to the position chosen, accessibility 
for replacement of fuselinks, and freedom from 
dampness and adverse conditions (if exposed to the 
weather or damp conditions, a distribution board must 
be of the weather proof type) The distribution boards 
shall not be more than 2 m above room floor level. 

5.2.4.2 Where distribution boards (which are fed from 
a supply exceeding 230 V) feed circuits with a voltage 
not exceeding 230 V then precautions must be taken 
to avoid accidental shock at the higher voltage between 
the terminals of two lower voltage boards. Where the 
voltage exceeds 230 V, a clearly visible warning label 
must be provided, worded "400/415 V BETWEEN 
ADJACENT ENCLOSURES". These warning notices 
should be fixed on the outside of busbar chambers, 
distribution boards or switchgear, whenever voltage 
exceeding 230 V exists. 

5.2.5 Feeding Distribution Board 

When more than one distribution board is fed from a 
single submain cable or from a rising bus bar trunking, 
it is advisable to provide local isolation near each 
distribution board {see Fig 4). It is also good practice 
to provide a local isolator for all distribution boards 
which are situated remote from the main switchboard 
{see Fig. 5). If the main or submain cables consist of 
bare or insulated conductors in metal trunking, it is 
very often convenient to fit the distribution board 
adjacent to the rising trunking, and to control each with 
fusible cutouts or switchfuse. 

5.2.6 Circuit Charts and Labelling 

The diagrams, charts or tables shall be provided to 
indicate for each circuit: 

a) The outlets served, 

b) Size and type of cable, and 

c) Rating of fuse or protective device. 

These should be fixed in, or in the vicinity of the 
distribution board, and fitted in glazed frames or in 
plastic envelops for protection. 

5.2.7 Marking Distribution Boards 

a) All distribution boards should be marked with 
a letter or number, or both, preferably with 
the prefix *L' for lighting, 'S' for socket and 
'P' for power. 

b) They should also be marked with the voltage 
and the type of supply, and if the supply exceeds 
230V a DANGER notice must be fixed. 

c) When planning an installation, a margin of 
spare fuseways should be provided usually 
about 20 percent of the total. 



48 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



FINAL CIRCUITS 




MAIN FUSeSWITCM 



NOTE — The cables feeding the ring will share the load and may therefore be reduced accordingly. This arrangement enables the ring 
to be broken by one of the isolators in the event of a fault a one end of the ring, in which case the load must be reduced. 

Fig. 4 Single Line Diagram of a Typical Ring Main Feeding Six Distribution Boards 



O- 



6-WAY 15A 

DISTRIBUTION 

SOARDS 



I I 



SPARS 
WAYS 

Ha™ 



fOWAV 9 $OOA 

D1STRI3UTION 

8QARD 



a 






MAIN 
J SWITCH 



NOTE — It is recommended that distribution boards located remote from main switchgear be provided with local isolators. 

Fig. 5 Single Line Diagram Showing Six Final Distribution Boards Fed by 
Radial Submains from a Main Distribution Board 



PART 1 GENERAL AND COMMON ASPECTS 



49 



SP 30 : 2011 



d) Metal distribution boards should be provided 
with plugged holes to enable additional 
conduits or multicore cables to be easily 
connected in future. 

53 Approximate Estimates of Allowable Voltage 
Drop in Different Farts of Wiring System of a Large 
Building 

There is no hard and fast rule in this respect. Ordinarily, 
however, in a lighting circuit containing lights and fans, 
the total voltage drop is kept within 3 percent of the 
declared voltage. The maximum allowable voltage drop 
is 1 V from main fuse to main distribution board, 4.5 V 
from main distribution board to each sub-distribution 
board and 1.5 V in each final sub-circuit. The voltage 
drop in the connection line of a pump motor in a house 
may go up to 7.5 percent of the declared voltage, but 
as is the case with a lighting circuit, it is recommended 
to keep this drop within 3 percent, if possible. 

5.4 Correct Estimation of Sizes of Cables 

5.4.1 If the size of cable is determined on the basis of 
total load connected in the circuit, that is, on the basis 
of sum of wattage of all lamps, fans, wall-plugs, etc, 
the size will be very large. However, all lamps, fans, 
wall-plugs etc, may not be in use simultaneously at a 
given time, and it is possible that all the points are not 
loaded to their full capacity. For these reasons it is 
considered to be sufficiently accurate if an estimate is 
prepared according to 5.1.1.7 and the criteria of 
considering two-thirds of total wattage of the circuit, 
that is, the total wattage of every final sub-circuit is 
obtained by adding up the wattage of individual loads 
connected to that circuit and two-thirds of this total 
wattage should be taken into consideration for 
determining the size of cable to be used for this sub- 
circuit. But the current corresponding to this wattage 
must not be less than the current drawn by the single 
maximum wattage point. If a sub-circuit has only one 
point, cable suitable for full load current of that point 
is to be used. However, if a sub-circuit has three 6 A 
plug-sockets, the size of the cable can be determined 
on the basis of two-thirds of 180 W (that is, 120 W). 



The above applies to ordinary dwelling-house, but not 
to all buildings. Three-fourths of the total wattage is to 
be considered for hotels, boarding houses etc, and nine- 
tenths for office etc. For the auditorium of cinema, theatre 
etc, cables suitable for full connected load are to used. 

5.4.2 If in a house there is electric cooker or electric 
oven, full load up to 10 A and one-half of any extra 
load (in excess of 10 A) should be taken into account. 
The load of every sub-circuit is thus calculated, and 
the current drawn by a sub-distribution board is 
determined. 

5.4.3 The load of wall-plug connected to a sub- 
distribution board in a dwelling house where there are 
wall-plugs of various sizes will be the full-load of the 
plug drawing maximum current plus four-tenths of all 
the remaining plugs. In hotels etc, three-fourths of the 
total load of all the remaining plugs have to be added 
to the full-load of the plug drawing maximum current. 

a) At first currents for the sub-circuits are to be 
determined, one by one. 

b) Sizes of fuse should be determined according 
to capacity to continuously carry the 
respective current. 

c) The size of cable for each sub-circuit is 
determined according to the current drawn by 
that sub-circuit. 

d) Finally, the sizes of flexible cord and wall- 
socket for the respective sub-circuit to be 
determined. 

5.5 Diversity and Maximum Demand 

In determining the maximum demand of an installation 
or parts thereof, diversity may be taken into account. 

Table 2 gives guidance on diversity, but it is emphasized 
that the calculation of diversity would have to take into 
account several factors which would need special 
knowledge and experience. By consulting Table 2, a 
reasonable estimate can be obtained as to what the 
maximum load is likely to be, but it must be stressed 
that each installation must be dealt with on its own 
merits. 



Table 2 Typical Allowances for Diversity 
(Clause 5.5 ) 



SI Purpose of Final Circuit Fed from 
No. Conductors or Switchgear to 
which Diversity Applies 



(1) 



(2) 



Type of Premises 



Individual house- hold 
installations, including 
individual dwelling of a block 
(3) 



Small shops, stores offices 
and business premises 

(4) 



Small hotels, boarding houses 
etc 

(5) 



66 percent of total current 90 percent of total current 75 percent of total current 
demand demand demand 



i) Lighting 



50 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 
Table 2 — (Concluded) 



_0) (2) (3) (4) (5) 

ii) Heating and power [also see SI. No. 100 percent of tota] current 100 percent of full load of 100 percent of full load of 
(iii) to (iv) below] demand upto 10 A largest appliance largest appliance 

+50 percent of any current +75 percent of remaining +80 percent of second largest 
demand in excess of 10A appliances appliances 

+60 percent of remaining 
appliances 
iii) Cooking appliances 10A 100 percent of full load of 100 percent of largest 

+30 percent of full load of largest appliance appliance 

connected cooking appliances +80 percent of full load of +80 percent of full load 1 of 
in excess of 10 A + 6 A if second largest appliance second largest appliance 
socket-outlet incorporated in +60 p ercent of M load of +60 percent of full load of 
umt remaining appliances remaining appliances 

iv) Motors (other than lift motors which 100 percent of full load of 100 percent of full load of 

are subject to special consideration) largest motor largest motor 

+80 percent of full load of +50 percent of full load of 
second largest motor remaining motors. 

+60 percent of full load of 
remaining motors 

v) Water heater (instantaneous type 1} ) 100 percent of full load of 100 percent of full load of 100 percent of full load of 

largest appliance largest appliance largest appliance 

+100 percent of full load of +100 percent of full load of +100 percent of full load of 
second largest appliance second largest appliance second largest appliance 

+25 percent of full load of +25 percent of full load of +25 percent of full load of 
remaining appliances remaining appliances remaining appliances 

vi) Water heaters (thermostatically No diversity allowable 2) +25 percent of full load of 

controlled) remaining appliances 

vii) floor warming installations No diversity allowable 2) 

viii) Water heaters thermal storage space No diversity allowable 2) 
heating installations 

ix) Standard arrangements of final 100 percent of current demand 100 percent of current 
circuits in accordance with IS 732 of largest circuit demand of largest circuit 

+40 percent of current demand +50 percent of current 
of every other circuit demand of every other circuit 

x) Socket outlets other than those 100 percent of current demand 100 percent of current 100 percent of current demand 

included in SI No. (ix) above and of largest point demand of largest point of largest point 

stationary equipment other than ^q percent of cumnt demand +?5 percent of current +75 percent of current demand 

those listed above Q f ever y ot h er point demand of every other of every point in main rooms 

point (dinning rooms, etc) 

+40 percent of current demand 
of every other point 



i) 



2) 



For the purpose of the table an instantaneous water heater is deemed to be a water heater of any loading which heats water only while 
the tap is turned on and therefore uses electricity intermittently. 

It is important to ensure that the distribution boards are of sufficient rating to take the total load connected to them without the 
application of any diversity. 

An example of estimation of maximum demand for a domestic installation with a single tariff is given below: 

Connected Load Expected Maximum Demand 

Installed lighting — 10A 66 percent of installed load = 6.6A 

Installed fixed heating— 30A 100 percent of first 10 A plus = 20A 

50 percent of excess of 10 A 
Installed general-purpose socket-outlet — 40A 100 percent current demand of largest = 28 A 

circuit (20A) plus 40 percent current 

demand of other circuits (8A) 
Installed cooker — 45A 10A plus 30 percent of full load of = 22A 

remaining connected appliances plus 6A 

for socket in unit 

Total 125A 76.6A 

PART 1 GENERAL AND COMMON ASPECTS 51 



SP 30: 2011 



In this case a 100A main switch should be provided. 
Unless it is anticipated to increase the load considerably 
in the foreseeable future, in which case a larger switch 
fuse should be installed. 

However, for a small restaurant where electric lighting 
and heating is installed, it would be most likely that 
the whole load will be switched on at one time and 
therefore the main switchgear must be suitable for the 
total installed load. 

5.6 MV/LV Busbar Chambers (400/230V) 

Bus bar chambers which feed two or more circuits must 
be controlled by a main disconnector (TP and N), or 
isolating links, or (three) fuses and neutral link, to 
enable them to be disconnected from the supply. 

5.7 Earthed Neutrals 

To comply with Indian Electricity Rules, 1956 no fuses 
or circuit-breakers other than a linked circuit-breaker 
shall be inserted in an earthed neutral conductor, and a 
linked switch or linked circuit-breaker shall be arranged 
to break all the related phase conductors. If this neutral 
point of the supply system is connected permanently 
to earth, then the above rule applies throughout the 



installation including 2-wire final circuits (see Fig. 6). 
This means that no fuses may be inserted in the neutral 
or common return wire and the neutral should consist 
of a bolted solid link, or part of a linked switch which 
completely disconnects the whole system from the 
supply. This linked switch must be arranged so that 
the neutral makes before, and breaks after the phases. 

5.8 General Design of Feeder Circuit, Distribution 
Circuit and Final Circuit 

5.8.1 Every distribution board must be connected to 
either a main switch fuse or a separate way on a main 
switch board. Every final circuit must be connected to 
either a switch fuse, or to one way of a distribution 
board. In either case the rating of the protective device 
must not exceed the current rating of the circuit cable. 

5.8.2 The circuit which is connected to single-way of 
switch board/sub-switch board or fuse/MCB distribution 
board for supplying current to one or more load point 
known as 'final circuit' . In the case of domestic and 
commercial supply, the suppliers' line or cable comes 
to the energy meter through supplier's scaled cut-out 
and from the meter it goes to consumer's main switch. 
This line is called 'supply main' or 'main line'. 



& SOUD W&UT9AL 
MMRV& 



OOUSLC POLf 

UNtttD &wtrcnt& 

WITH ftlNCU 
POU PVSC & 
SOU© MluraAl 




NOTE — When the neutral point of a supply or one pole of transformer on consumer's premises is earthed permanently, a fuse, non- 



linked switch or circuit-breaker is not permitted in the line connected to earth. 

Fig. 6 Single Pole Fusing 



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5.8.3 On account of heavy load in big factories of 
horizontal distribution, very often feeder line is drawn 
from the main incomer switch to busbar chamber of 
main switch board and the feeder line is called 'supply 
main' or 'main feeder'. If sub-switch board or 
distribution board is installed next in sequence to 
another sub-main switch, the feeder line upto sub- 
switch board or main distribution, the line from main 
switch board up to sub switch board or main 
distribution board is called 'sub-main feeder'. If main 
distribution board is installed next in sequence to sub- 
(main) switch board, the line upto main distribution 
board is called 'main distribution feeder' line. And from 
there line is drawn through different sub-busbar 
chambers of sub-switch boards to distribution boards, 
or from the main switch board and direct to main 
distribution boards. 

5.8.4 Also on account of heavy load in large buildings 
of vertical distribution, very often main feeder line is 
drawn from the main incomer switch to main busbar 
chambers and from there upto different sub-busbar 
chambers and or main distribution boards, the feeder 
line from consumer's main switch to busbar chamber 
that rises from the ground floor upto the top most floor 
in multistoried building is known as 'main raising 
main'. If sub-(main) busbar chamber or main 
distribution board is installed next in sequence in 
different floors through another submain switch, feeder 
line upto sub-(main) busbars or main distribution 
boards is called 'sub-main raising bars' and considered 
sub-main feeder line. If main distribution is installed 
next in sequence to sub-main busbars, the line upto 
main distribution board is called 'distribution busbar' 
and considered main distribution feeder line. Circuit 
lines drawn from main distribution boards upto final 
circuit fuse districution boards /MCB distribution 
boards may be as 'sub-main distribution feeder'. 

5.8.5 Every circuit line which runs from final circuit 
fuse distribution board towards load points is called 
'final circuit'. Sometimes a circuit line may go to a 
load point from a main distribution board/main 
distribution busbar chamber, a sub-main switch board/ 
sub-main rising main, a main switch board /main rising 
main etc; in that case every line is regarded as a final 
circuit. 

5.8.6 Every final circuit must come out of a separate 
way of a (final circuit) distribution board. Where there 
is only one final circuit, it may be connected directly 
to the main switch board. 

5.8.7 Wiring of every final circuit will be completely 
separated from that of another final circuit which can 
be on or off with a single-pole switch. Care must be 
taken to see that every pair of live or neutral wires are 



kept together properly in order in the distribution board 
for the convenience of testing or disconnecting current 
flowing towards load points must not exceed the circuit- 
carrying capacity of wires used for final circuit. 

5.8.8 Use of Plug Point with Lamp Circuit 

In a house wiring, usually lamp, wall-plug etc., are 
connected to the same circuit. The actual limit of the 
current that the cables used in the wiring can safely 
carry should be known. Considering the final circuit 
which includes discharge lamps, the sum total of 
currents taken by all discharge lamps together must 
not exceed the current carrying capacity of the final 
circuit. If the lamps are lighted by means of only the 
normal circuit, current carrying capacity of the final 
circuit should be 1.256 times the total current of all 
the lamps together. 

If in a final circuit both incandescent lamps and 
inductor-lighted discharge lamps are used, 

(Power taken by inductor- + (Power taken by incan- 
lighted discharge lamps x 2) descent lamps x 1) 
Line voltage 

Must not exceed the current carrying capacity of the 
final circuit. 

5.8.9 Exception in Case of Temporary Wiring 

In case of temporary load points where bayonet holders 
for lamps have been used, total power demand of load 
must not exceed 1 000 W per final circuit. 

5.8.10 Splitter Unit 

This kind of distribution board is very much in use 
now-a-days. This board can be installed anywhere and 
is known as 'splitter unit' or 'splitter box'. The unit is 
prepared by setting a pair of main switches as well as 
a pair of main fuses or a single fuse inside a cast iron 
box. An external handle is attached to the body of the 
box. It is so arranged that the cover of the box cannot 
be opened when the switch is in the on position or the 
switch cannot be switched on when the cover is open, 
that is the cover cannot by any means be opened unless 
the switch is off. It is for this arrangement that the unit 
is quite good from the point of view of safety. The box 
is also known as Iron-clad Switch-Fuse Box. The 
switch-fuse box is installed at a point where from 
consumer's zone starts. Cables are drawn from the 
switch and connected to the bus-bars of a fuse board. 
This is the main distribution board, Now-a-days iron- 
clad fuse-box is very much in use. A screw is attached 
to the body of this box. The risk of electric shock is 
avoided by connecting earth wires to that screw. The 
box is to be earthed by two separate and distinct earth 
connections. 



PART 1 GENERAL AND COMMON ASPECTS 



53 



SP 30 : 2011 



5.8.11 Lamps of the Same Room are Supplied from 
More Than One Final Circuit Distribution Boards 

When outlets from a sub-distribution board or a fuse 
board are divided into 'ways' and each final sub-circuit 
is connected to a separate way, the advantage is that in 
the event of a short-circuit in anyone sub-circuit, the 
other sub-circuits remain unaffected and continue to 
function normally. But if a fault occurs in a distribution 
board, all the sub-circuits coming out of it are affected. 
There are some places such as hospital, operation 
theatre; cash room in a bank, engine room, workshop 
etc, where the entire room cannot be allowed to be 
dark under any circumstance. A lot of risks may have 
to be faced if such places suddenly become totally dark. 
Wherever special attention must be paid to avoid any 
inconvenience in business, every room is equipped with 
more than one lamp and these are invariably taken from 
different ways. Even sometimes these lamps are 
supplied from fully separate distribution board. 
Suppose the wiring of a three-storeyed building is to 
be done in such a way that no room of that building 
shall be totally dark (except in the event of discontinuity 
of supply). In that case there must be a separate sub- 
distribution board in each floor. But it is not that the 
sub-distribution board will control the load points of 
that floor only. Depending on the convenience of a 
circuit, sub-distribution board in the lower floor will 
supply power to some lamps etc, of the lower floor 
and to some lamps etc, of the upper floor. Every room 
will be provided with two sets of cables — one set will 
be supplied from sub-distribution board of the upper 
floor and the other set will be supplied from sub- 
distribution board of the lower floor. With these 
arrangements if a fault develops in a sub-distribution 
board, there is no possibility of any room becoming 
totally dark. In such cases, operation theatre etc, are 
provided not only with connection from separate 
distribution boards but with alternative source of supply 
such as gas plant or charged battery. 

5.8.12 Pilot Lamp 

Arrangements should be made for fixing a bracket 
above each main board and for connecting a 20 W lamp 
on it. Cables connecting this lamp will come out 
directly from the bus bars of the board through a 
separate switch arid fuse. This lamp is called a Pilot 
Lamp. The purpose behind this arrangement is to keep 
the main board always illuminated so that fuse etc, can 
easily be changed. 

5.8.13 Arrangements for Taking Cable Connections 
from One House to Another 

If wiring is to be done to supply current from one house 
in which consumer's main switch has been installed to 
another house, whichever of the following 



arrangements is suitable (for a particular case) is to be 
adopted for the wiring and its protection: 

If the distance between the house in which the main 
meter board has been installed and the other house (for 
example garage, servant's room etc) does not exceed 
3 m and if there be no thoroughfare between the two 
houses, electric lines may be drawn from the former to 
the latter through a galvanized iron (G.I.) pipe of 
suitable dimensions at a height of at least 2.5 m above 
the ground level. Also the G.L pipe has to be properly 
earthed. But in case the distance between the two houses 
exceeds 3 m or if there is a thoroughfare between them, 
a separate main or sub-main has to be drawn from one 
house to another by means of weather-proof cables tied 
up with G.I. bearer wire (see Fig. 7A). 

If current is to be taken from one house to another by 
means of cleat wiring, the cable used in the wiring will 
be weather-proof. This is also known as H.S.O.S. 
(House Service Overhead System) cable. Use of cable 
with 'polychloroprine' sheath or PVC cable or cable 
with PVC sheath is also approved by many. This 
arrangement of drawing a supply line is allowed up to 
a distance of 3 m between two buildings. Using cables 
as described above and drawing these cables over a 
separate catenary wire or using those cables which have 
in-built bearer wires (at the time of manufacture), the 
supply line may be drawn. 

Other methods of drawing cables over bearer wires 
are also in use, one of these methods is shown in 
Fig. 7B. In this method a piece of leather strap loops a 
hard rubber- sheathed cable at certain intervals for 
hanging it, while the upper part of the strap is fastened 
to the catenary wire by means of wire hook. This is 
also an arrangement for taking a supply cable from 
one building to another. If such a cable, as has in-built 
bearer wire, is used, the limit of distance between two 
buildings will depend upon the load-bearing capacity 
of the bearer wire. 

Besides these a cable may be drawn from one house to 
another as shown in Fig. 7C. Main earth pit should be 
at least 1.5 m away from the building. 

5.8.14 Identification of Cables and Conductors 

IS 1 1353 gives guidance on uniform system of marking 
and identification of conductors and apparatus 
terminals (see Table 3). Colours of the cores shall be 
as per relevant Indian Standard for cables. The 
following shall be ensured: 

a) Non-Flexible Cables and Bare Conductors — 
Every single core non-flexible cable, and 
every core of twin or multicore non-flexible 
cable used as fixed wiring shall be identifiable 
throughout its length by appropriate methods. 



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7 A Gl Bearer Wire Stretched Between Two Houses and Supply Cable Tied- 
Up with this Wire by Means of Link Clips 






7B Leather Strap Loops for Hanging Hard Rubber-sheathed Cable at Intervals 

NOTE — Leather strap loops are used for hanging hard rubber- sheathed cable at intervals while the upper part of the strap is fastened 
to the catenary wire by means of wire hook 




Earth 



7C Drawing of Supply Cable from One House to Another 
Fig. 7 Arrangements for Taking Cable Connections from One House to Another 



b) Rubber or PVC Insulated Cables — Core f) 
colours to be in accordance with respective 

Indian Standard or colour sleeves at the 
termination of these cables. 

c) Multicore PVC Cables — If colouring of g) 
cores is not used, then cores to be identified 

in accordance with relevant Indian Standards. 

d) MI Cables — At the termination of these 
cables, sleeves shall be fitted. 

e) Bare Conductors — To be fitted with sleeves 

or painted. h) 

PART 1 GENERAL AND COMMON ASPECTS 



Colour coding of fixed wiring cables applies 
to all wiring up to the final distribution board, 
and also for circuit wiring, except that red may 
be used for any phase. 
When wiring to motors the colours specified 
in Indian Standard should be used right up to 
the motor terminal box. For slipring motors 
the colours for the rotor cables should be the 
same as those for the phase cables, or could 
be all of one colour except black or green. 
For star delta connections between the starter 



55 



SP 30 : 2011 



and the motor, use red for Al and A0, yellow 
for Bl and BO, and blue for CI and CO. The 
"1" cables should be marked to distinguish 
them from the "0" cables. 

j) For 2-wire circuits, such as for lighting or 
sockets, the neutral of middle wire must 
always be black, and the phase or outer wire 
(whichever phase it is derived from) should 
be red. 

k) For lighting the red wire will always feed the 
switch, and a red wire must be used from the 
switch to the lighting point. 

For flexible cables and cords the distinctive colours 
are not the same as for fixed wiring, and the colours of 
these are given in Table 4. 



5.8.15 Sub-main Cables 

Sub-main (feeder) cables are those which connect 
between a switch fuse/MCCB feeding sub distribution 
boards of main switchboard, to incomer of subsidiary 
main switch board or direct to a main distribution 
board. The size of these cables will be determined by 
the total connected load which they supply, with due 
consideration for diversity and voltage drop, and the 
other factors described in Wiring Regulations. 
Sub-main cables may be arranged to feed more than 
one distribution board if desired; they may be arranged 
to form a ring circuit, looping from one main 
distribution board to another. Where a sub-main cable 
feeds more than one distribution board in a ring circuit, 
its size must not be reduced when feeding the second 



Table 3 Colour Identification of Cores of Non-fiexible Cables and Bare Conductors for Fixed Wiring 

(Clause 5.8.14 ) 



SI No. 



0) 



Function 



(2) 



Colour Identification of Core of Rubber or PVC 

Insulated Non-flexible Cable, or of Sleeve or Disc to 

be Applied to Conductor or Cable Code 

(3) 



i) 
ii) 
iii) 
iv) 
v) 
vi) 
vii) 
viii) 
ix) 

x) 

xi) 

xii) 

xiii) 



Protective or earthing 

Phase of ac single-phase circuit 

Neutral of ac single or three-phase circuit 

Phase R of 3-phase ac circuit 

Phase Y of 3-phase ae circuit 

Phase B of 3-phase ac circuit 

Positive of dc 2-wire circuit 

Negative of dc 2-wire circuit 

Outer (positive or negative) of dc 2-wire circuit derived from 3 wire 

system 

Positive of 3-wire system (positive of 3-wire dc circuit) 

Middle wire of 3-wire dc circuit 

Negative of 3-wire dc circuit 

Functional earth-telecommunication 



Green and yellow 

Red [or yellow or blue (see Note 1)] 

Black 

Red 

Yellow 

Blue 

Red 

Black 

Red 

Red 
Black 
Blue 
Cream 



NOTES 

1 As alternative to the use of red, if desired in large installations, up to the final distribution board. 

2 For armoured PVC-insulated cables and paper-insulated cables, see relevant Indian Standard. 



Table 4 Colour, Identification of Cores of Flexible Cables and Flexible Cords 

(Clause 5.8.14) 



SI No. 


Number of Cores 


Function of Core 


(1) 




(2) 


(3) 


i) 


1 




Phase 

Neutral 

Protective or earthing 


ii) 


2 




Phase 
Neutral 


iii) 


3 




Phase 

Neutral 

Protective or earthing 


iv) 


4 


or 5 


Phase 

Neutral 

Protective or earthing 



Colour(s) of Core 

(4) 



Brown 
(Light) Blue 
Green and yellow 
Brown 

(Light) Blue 
Brown 

(Light) Blue 
Green and yellow 
Brown or black 
(Light) Blue 
Green and yellow 



} Certain alternatives are allowed in Wiring Regulations. 



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or subsequent board, because the cable must have a 
current rating not less than the fuse or circuit breaker 
protecting the sub-main. If a fuse or circuit-breaker is 
inserted at the point where a reduction in the size of 
the cable is proposed, the reduced size of cable may 
be used, providing that the protective device is rated 
to protect the cable it controls. 

5.8.16 Protective Multiple Earthing (PME) 

5.8.16.1 Protective multiple earthing system uses the 
protective conductor as a combined earth/neutral 
conductor. It is sometimes used where there is overhead 
distribution, and where it is difficult to obtain a 
sufficiently low earth resistance from supply 
transformer to the consumer's terminal. In such a case 
the neutral conductor is also the earth conductor and it 
is bonded to earth, not only at the transformer position, 
but also at the consumer terminal position. The 
condition of approval for this system contain very 
stringent requirements. The wiring for consumers 
installations, including sub-mains and circuits wiring 
may (if approved) be carried out on the PME system. 
Some of the requirements for consumer's installation 
are as follows: 

a) The supply undertaking shall be consulted to 
determine any special requirements 
concerning the size of protective conductors. 

b) All precautions must be taken to avoid the 
possibility of an open circuit in the neutral 
conductor. 

c) Bonding leads must be connected to the 
earthing terminals of all metal structures, 
metal pipes and other metal services that are 
(or may reasonably be expected to become) 
in electrical contact with the general mass of 
earth, and that are so situated that 
simultaneous contact may reasonably be 
expected to be made by any person with such 
structures, pipes or other metal work on the 
one hand, and with the exposed non-current- 
carrying metalwork of the consumer's 
installation, or any metal work in electrical 
contact therewith, on the other hand. 

d) Earth electrodes shall be provided at points 
not less remote from the transformer than the 
most remote service line or connection point, 
and at such other points as will ensure that 
the resistance to earth in the neutral conductor 
is satisfactory and the protection system 
operative. The overall resistance shall not 
exceed 20 times. 

e) There shall be a wire connection from the 
neutral earth conductor to both the neutral and 
the earth terminal of every socket outlet. 



Wiring from plugs or spur units to lamps and 
appliances shall be carried out by a phase 
conductor, a conductor and a separate earth 
conductor, 
f) There shall be electrical continuity of the 
neutral earth sheathing of multicore armoured 
cables. All connections and joints shall be 
made in accordance with the 
recommendations of the cable manufacturer. 
At every joint in the outer conductor (that is 
neutral earth) and at terminations, the 
continuity of the conductor shall be ensured 
by bonding conductor additional to the means 
used for sealing and clamping the outer 
conductor. 

5.8.16.2 The use of a PME system in petrol filling 
stations is specifically prohibited. The reason for the 
prohibition is to prevent the risk of electrical return 
currents flowing back to earth through the metallic 
parts of the underground supply pipes and storage 
tanks. Special armoured multicore cables may be used 
for the PME system. Such cables may be with XLPE 
(cross linked polyethylene) insulation, Aluminium 
conductors and sheath are used, and the cables have a 
PVC oversheath. The armouring in these cables is laid 
upon such a way that sufficient amount can be pulled 
away from the cable without the necessity of cutting 
it, to enable access to the phase conductor for the 
purpose of jointing. These special cables are only 
manufactured in minimum lengths of about 200 m, and 
it may not be economical to employ the PME system 
for sub-main cables when only short runs are involved. 

5.8.16.3 Circuit wiring 

a) Circuit ring for PME system may also use a 
common neutral earth (CEN) conductor, but 
in some instances this may not result in any 
cost savings. 

b) For mineral-insulated copper sheathed 
systems the outside sheathing lends itself 
readily to the system, but special glands 
should be used to ensure satisfactory low 
impedance in the earth conductor. 

c) For screwed-conduit systems it is sometimes 
difficult to guarantee satisfactory low 
impedance in the conduit system during the 
life of the installation, and it is recommended 
that a circuit protective conductor (CPC) 
neutral conductor be drawn into the conduit. 

d) The same recommendation applies to wiring 
is steel trunking, because it is imperative that 
there be no risk during the life of the 
installation that an open circuit, or a high 
resistance joint, could occur. 



PART 1 GENERAL AND COMMON ASPECTS 



57 



SP 30 : 2011 



e) Before planning any PME installation careful 
study must be made of the actual conditions 
of approval issued by the concerned 
regulatory authority. 

5.9 Computer Data Transmission and Control 
System 

Cables required for data transmission and control 
systems are those that are required between the 
computer and the outstations and those used between 
the machine and the associated peripheral equipment. 
Generally, the field wiring is multicore and may have 
screening applied to each core, to each pair or, simply, 
overall. There is a large range of cables used by different 
computer manufacturers. One of the commonly used 
cables for peripheral equipment is the ribbon form 
which is also produced as multicore cable, with and 
without screening and various types of insulation. 
Although ribbon cables are produced in widths upto 
approximately 80 mm and with over 60 cores, they are 
extremely thin and, therefore, flexible. 

5.10 Multiplex Systems 

One of the advantages gained by the use of electronic 
equipment is that the amount of field wiring required 
is far less, in both quantity and size, than for the earlier 
power circuitry entailed by mechanical relay systems. 
Even further improvements are made possible by the 
use of multiplexing systems, that is, the ability to 
convey a large number of signals each way along the 
same conductor, and these are, therefore, particularly 
suitable for installations requiring a large number of 
outstations, whether for data transmission or process 
control. Optical fibre cables provide further advantages 
for light-current installations of all types; they have 
low attenuation and high bandwidth, which reduces 
the necessity for repeaters, and are not subject to 
interference from heavy electrical equipment. In 
hazardous areas, optical fibres give even greater safety 
than intrinsically safe circuits as the form of energy 
transmitted is, of course, light waves and not current. 

5.11 Domestic Systems 

5.11.1 The smaller domestic type of installation is 
adequately catered for with twin and circuit protective 
conductor (CPC) PVC cables or single-core PVC cable 
in some form of enclosure; the installation of the first 
is less labour-intensive than conduit work although the 
second provides better mechanical protection. Due to 
the amount of space that is occasionally available 
between floorboards and ceilings (modern construction 
methods include solid floors) and in lofts, installation 
is relatively simple and protection is rarely necessary 
for horizontal runs. Where droppers are required for 
switches and wall-fittings, however, it is essential to 



provide oval conduit or capping over the cables. 
Although PVC has a much longer anticipated life than 
the previously used rubber covered cables, MICC is a 
suitable alternative which has an even longer life. It is 
not commonly used on very small installations except, 
possibly, for exterior lighting or feeds to remote 
buildings. 

5.11,2 To avoid undue disruption and damage to 
existing floorboards, plastering, etc, a number of 
enclosed surface systems are available which 
incorporate mini-trunking, dado-trunking and cornice- 
trunking. For each system, accessories are available 
for accommodating different types of outlet and for 
negotiating corners, doorways, etc, a correctly designed 
installation is effective and relatively inconspicuous, 
although even where obvious, such as across ceilings, 
it presents an aesthetically pleasing appearance. 

5.12 Telephone Cables 

As the user finds it more convenient to install his own 
internal telephone systems, a large range of cables 
available for the purpose. The conventional type of 
multipair or multitriple cable consists of tinned copper 
conductors, PVC-insulated and sheathed with, in some 
cases, a non-metallic rip-cord laid under the sheath to 
simplify stripping while, for under-the-carpet 
installations or situations where the conventional round 
cables are inconvenient or too bulky, ribbon cables are 
again available with upto 50 ways. Where such cables 
may be subject to damage or heavy traffic, such as 
under floor coverings, ribbon cables insulated with 
cross-linked PVC (XLPVC) which is more robust than 
standard PVC may be used. XLPVC are different from 
XLPE-insulated cables which, among other 
advantages, have fire-retardant properties. 

5.13 Cable Jointing and Termination 

5.13.1 Although the methods employed for jointing 
and terminating cables of all types have been 
simplified, largely due to the use of improved materials 
for insulation and sheathing, the importance of utilizing 
correct techniques and methods cannot be too strongly 
emphasized. All joints and terminations introduce 
potentially dangerous points; in power circuits a faulty 
joint will lead to local hot-spots with ultimate failure 
of the cable, while in light- current installations for 
process control, data transmission and 
communications, a high resistance connection (dry 
joint) can prevent equipment from operating 
satisfactorily. 

5.13.2 Multicore cables, whether for mains, voltages 
or light-current duty, generally present the greater 
problem as the crutch, that is, the point at which 
conductors are splayed out from the normal formation, 



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constitutes a naturally weak area in which air may be 
trapped if a termination or joint is not correctly formed, 
leading to breakdown at a later stage. 

5.13.3 Single-core cables should, preferably, never be 
jointed, but where this is essential it should be effected 
only in purpose-made joint boxes equipped with 
suitable mechanical or compression- type connectors. 
These may be of the ferrule type with pinching screws 
or, as with terminators, bolted clamps requiring the 
bare conductor to be either wound around the bolt 
between shaped washers or enclosed in crimped type 
terminals which are then threaded over the screw thread 
and clamped. It is essential with all types of stranded 
cable to ensure that every strand is included in the joint 
or termination and, particularly with aluminium 
conductors, to follow cable manufacturers' 
recommendations for tightening torques. Aluminium, 
although lighter in weight and less expensive than 
copper, unfortunately has a higher co-efficient of 
expansion and this has, at times, caused connections 
to slacken shortly after commissioning. It is therefore 
advisable for the installer of aluminium cables to 
recheck all clamp-type connections after electrical load 
has been applied. This does not imply, however, that a 
similar procedure is unnecessary with copper 
conductors but that it may not be so essential provided 
that connections are fully checked in the first instance. 

5.13.4 Crimped terminals are quite adequate for the 
smaller, relatively lightly loaded cables but, otherwise, 
compression sleeves and lugs, provided that the 
recommended torques are applied, are unlikely to give 
rise to problems during the life of a cable under the 
most arduous circumstances. 

5.14 Special Cabling Requirements 

5.14.0 Although PVC insulated cables are suitable for 
most of the general wiring requirements in domestic, 
commercial and industrial situations, circumstances 
may dictate, either through technical necessity or 
statutory demands, that further precautions are 
necessary to prevent the possibility of danger or to give 
increased security, as detailed below. 

5.14.1 Lighting 

The two main areas of concern are related to heat build- 
up in luminaries and surges created by discharge 
lighting. In totally enclosed luminaries, high 
temperatures may arise due to the lack of ventilation. 
Though luminaires complying with the relevant Indian 
Standards take into account the temperature rise, 
however, during installation of luminaires it should 
ensured that wiring in proximity to the fittings is 
suitable. Discharge-type fittings may entail the use of 
higher current rated cables to avoid unnecessary 
temperature rises. The effects of high discharge 



currents during switching operations may have more 
drastic effects by causing a cable to disintegrate 
completely. Some cables are susceptible to current and 
voltage surges which may be avoided by the use of 
current limiting devices. Where electrical equipment 
in normal operation has a surface temperature sufficient 
to cause a risk of fire, suitable methods of protection 
should be adopted. 

5.14.2 Emergency Lighting 

Emergency lighting is very critical for at hospitals, 
theatres, hotels, factories, offices, shops, cinemas and 
certain specified places of entertainment and practically 
all types of premises excluding houses. Generally, the 
cable installation for an emergency lighting system 
should comply with Wiring Regulations but care must 
be taken to ensure that all wiring possesses inherently 
high resistance to attack by fire and adequate 
mechanical strength. This allows the use of various 
standard types of cable, provided that suitable means 
of protection are employed. When emergency 
luminaries are supplied from a remote source, the 
wiring system must be mechanically separated from 
other systems by rigid and continuous partitions of 
non-combustible materials. Consequently, 
multicompartment enclosures are suitable, also mineral 
insulated copper clad cables without further 
precautions. Segregation is not a requirement when 
self-contained luminaries are installed, as a failure of 
the supply will only cause them to operate. Precautions 
to be taken at the source of supply for an emergency 
lighting system are that cables between the source and 
a battery charger combination should be a fixed 
installation, which precludes plugs and sockets, while 
those cables from the battery to a protective device, 
that is the load circuit cables, must be separated from 
each other and not enclosed within metal conduit, 
ducting or trunking. Segregation must also be applied 
between the dc and any ac cables. 

5.14.3 Fire Alarms and Detection 

The requirements in the previous section regarding 
mechanical protection, high fire resistance and 
segregation, etc apply. Where high frequency circuits 
are installed, adequate screening is applied between 
the different circuits in order to avoid false alarms. 

5.14.4 Power System 

5.14.4.1 Some of the problems arising in the installation 
of power cables are high or low ambient temperatures, 
grouping, thermal insulation, type of protective device 
employed and voltage drop considerations. Under 
normal circumstances, correctly chosen protective 
devices are adequate to deal with disruptions such as 
overloads, short-circuits and earth-faults on low voltage 
systems but, on high voltage networks, transients may 



PART 1 GENERAL AND COMMON ASPECTS 



59 



SP 30: 2011 



occur which create high stresses on cable insulation 
and therefore, it may be advisable to install screened 
cables which have the effect of grading such stresses 
between cores or between cores and earth. 

5.14.4.2 The handling and installation of all types of 
cable is an important consideration. Some PVC cables, 
for instance, should not be installed during 
temperatures below 0°C as flexing will damage the 
insulation, while high temperatures will soften the 
PVC, causing it to strip if pulled into conduit, ducting, 
etc. Damage may also be caused to cables by drawing 
them into rough-edged enclosures, for example burred 
conduits, over stony surfaces or bending them tighter 
than the recommended radii. Large armoured cables 
are impressively strong, but even these, when being 
drawn into ducts, may be damaged if the correct type 
of grip-sleeve (or sock) and hauling equipment is not 
used, as too high a torque may stretch the cable cores 
or strip off the insulation and sheathing. 

5.14.4.3 Particularly with the smaller armoured cables, 
if armouring is to be used as the protective conductor, 
the impedance must be checked to ensure that it 
complies with the relevant requirements; otherwise 
additional conductive material must be incorporated 
in the protective circuit. 

5.14.5 Control and Instrumentation 

Modern systems for control and instrumentation utilize 
electronic means (rather than power circuitry) which 
are more likely to be affected by low voltage systems, 
and precautions such as segregation and screening must 
be employed. Cables are available to suit all types of 
system but, as requirements vary between 
manufacturers of electronic equipment, advice should 
be sought at an early stage. The increasing use of 
multiplex systems and fibre-optics cables simplify 
installation work by reducing the number of cores 
required for the most complex systems and, in the case 
of the latter, eliminate completely the possibility of 
interference from other circuits. 

5.14.6 Hazardous Areas 

Danger in a hazardous area arises initially from the 
type of materials being processed rather than from the 
electrical installation, but a great degree of 
responsibility rests upon the designer to ensure that 
the installation does not contribute to the hazard by 
the introduction of flammable materials, high surface 
temperatures, arcs or sparks to the atmosphere. For 
these reasons, every care must be taken to avoid the 
overloading of cables or the inclusion of sheathing 
materials which easily burn and give off toxic gases. 

See IS 5572 for classification of hazardous areas and 
IS 5571 for selection of equipment in hazardous areas. 



Different degrees of hazard exist and, consequently, 
these affect the type of electrical installation, 
particularly with regard to equipment. It is essential, 
therefore, to ascertain which zone is applicable before 
commencing the electrical design, this information 
generally being available from the process plant user. 
See also Part 7 of the Code. 

6 WIRING SYSTEMS 

6.0 General 

6*0.1 The following systems are usually adopted for 
house wiring: 

a) Cleat wiring; 

b) Casing and capping wiring; 

c) Metal sheathed wiring (for example lead- 
covered wiring); 

d) Cab tyre sheathed (C.T.S.) or tough rubber 
sheathed (T.R.S.) wiring; 

e) PVC sheathed wiring; 

f) All insulated wiring — surface wiring and 
concealed wiring; 

g) Enclosed wiring system — conduit wiring and 
cable trunking; and 

h) Conduit wiring — steel, plastic and flexible. 

A particular type of wiring is selected for a particular 
place on the basis of type of work, place and expenses 
involved. Insulated wires are used in all systems of 
wiring. These systems have been named according to 
either constructional details of wires or modes of fixing 
these wires on the wall. The voltage grade of wires 
depends on supply voltage of the circuit, that is, the 
voltage grade of wires must not be less than the highest 
root mean square or effective value of supply voltage. 
In case of house wiring where working voltage 
normally does not exceed 250 V, wires of 250 V grade 
can be used. 

6.0.2 Size of Wires 

The wire used should have such cross-sectional area that 
when the maximum current drawn by the circuit flows 
continuously through it, the voltage drop between main 
distribution board and the farthest point of the lighting 
circuit does not exceed 3 percent of the supply voltage 
(in a 230 V circuit this drop is 3/100 x 230 = 6.9 - 7.0 
V). At the same time it should be ensured that the wire 
is not excessively heated when the maximum current 
flows continuously through it. Normally, the wire is not 
excessively heated when the amount of voltage drop 
remains within the limited value. 

If the size of a wire in a circuit has to be increased with a 
view to reduce the drop of voltage, it may be noted that 
the wire will carry as much current as has been determined 



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for the circuit to carry. Further, the size of a wire specified 
for a circuit must be suitable for continuous flow of current 
which is not less than the current-carrying capacity of the 
fuse of that circuit. Recommended current ratings for 
cables are as per IS 3961 . 

6.0.3 Protection of Wiring from Damage 

V.I. R. (vulcanized rubber) wire, plastic-insulated wire 
with or without braided cotton cover, C.T.S. (or T.R.S.) 
wire normally need not be further covered with separate 
covering. But situations and circumstances have to be 
taken into account, and if necessary, the outermost 
insulation has to be protected from probable damage. 

Where there is probability of conduit, duct, casing, etc, 
becoming hurtful, adequate arrangements have to be 
made to protect them. Where metal- sheathed wire or 
armoured cable is installed inside concrete or plaster, 
there is usually no need for further protection. However, 
depending upon site condition, sometimes additional 
arrangements may have to be made. 

Wires used for lift, hoist (an electrically operated 
machine used for lifting goods), etc, must be metal- 
sheathed [see also IS 4289 (Part 1) and IS 4289 (Part 2]. 
Where the wiring will pass under the floor, the wire 
should be so installed that it will not be damaged as a 
result of coming in contact with the floor or some fitting. 

Where a cable will enter the iron part of a house or the 
shed of a factory, every such entry should be provided 
with a bush in such a manner that the cable will not 
suffer abrasion from rubbing. 

Where the sheath of a C.T.S. cable made of rubber or 
some compound mixed with rubber will be exposed to 
direct sunlight, arrangements must be made to cover it 
with some special covering. If the sunlight comes 
through glass panes of windows, it is not a direct sunlight. 
Wiring should be done in as dry a place as possible. 

6.0.4 Permissible Temperature Rise of Ordinary 
Insulated Wires and Flexible Cables 

Ordinary insulated cables and flexible cables, which 
are not specially manufactured for withstanding 



excessive heat, should not be used in places where the 
temperature may exceed the limit given in Table 5. 

In cases where the temperature of lamp fittings and 
other accessories are excessively high, cables and 
flexible cords which are not specially made to 
withstand such high temperatures should not be 
brought near these fittings and accessories. Where there 
is probability of temperature exceeding 60°C, high 
temperature resisting cables like flexible cord, specially 
covered with conditioned asbestos, must be used. 
Further, they should be so connected that their 
temperatures do not exceed 85°C. If however, the 
flexible cord is connected with a portable heater with 
which there is not possibility of excessive rise of 
temperature, a temperature rise up to 66°C may be 
allowed, provided that the insulation of wires should 
remain covered with beads or insulating sleeves 
suitable for high temperature, and there is no 
dependence on rubber insulation of cable for the 
prevention of earth fault of cable conductors or short- 
circuit among them. These arrangements are to be 
specially provided for lamps rated 200 W or more and 
for immersion heater. 

Where a cable with rubber, PVC or polythene insulation 
or a flexible cord remains connected with bare 
conductor or a busbar, the insulation of the cable or 
cord should be peeled off and wires should remain bare 
for a length of about 1 5 cm from the point of connection 
even when the temperature of the bare conductor or 
the bus bar is 90°C. But in places where this cannot be 
done, the current flowing through the bare conductor 
or the busbar should be so reduced as not to allow a 
rise of temperature above 90° C. 

6.1 Cleated Wiring System 

6.1.0 Cleat wiring is one of the most economical 
methods of wiring. The wires remain exposed to view, 
and these wires are drawn through cleats made of 
porcelain or plastic or some other approved material. 
Cleat wiring is most suitable for temporary wiring. The 
wiring can be completed quickly and the wiring 
materials can be recovered easily while dismantling. 



Table 5 Permissible Maximum Temperature of Surrounding Space for Ordinary Insulated Cables 

(Clause 6.0.4 ) 



SI No. 



Types of Insulation 





*"*""" 




— % 




Cable 




Flexible Cable 


(1) 


(2) 




(3) 


i) 


Rubber 




Rubber 


ii) 


PVC 




PVC 


iii) 


Polythene 




— 


iv) 


Oil-soaked Paper 




— 


v) 


Cloth impregnated with 


varnish 


— 


vi) 


— 




Rubber or cloth mixed with 
conditioned asbestos 



Maximum Temperature of Surrounding 
Space or Space Inside Conduit Pipes 

(°C) 
(4) 



45 
45 
45 
75 
75 
80 



PART 1 GENERAL AND COMMON ASPECTS 



61 



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Moreover, additions and alterations as well as 
inspection of wiring system can be easily made. Cleat 
wiring is not recommended for damp places and also 
for permanent wiring. After a certain period of 
installation the wires sag at some places, dust and dirt 
collect over them and the whole of the wiring system 
may look shabby. 

6.1.1 The wires used are either vulcanized rubber 
insulated cables, single-core PVC or polyethylene 
cables, which can be used without further protection. 
Conductors should be visible all throughout a cleat 
wiring. 

6.1.2 The cleats are made in two parts, called base 
and cap. The base is grooved to receive the wire and 
the cap is placed over it, and the whole of it is placed 
on a wooden plug which is fixed into the wall. The 
cleats are tightened up on wooden plugs by means of 
wooden screws which also tighten the grip of the wires 
between two halves of the cleat. The cleats are usually 
of two types having two or three grooves so as to 
receive two or three wires. These cleats are shown in 
Fig. 8. 

6.1.3 Installation of Cleats 

a) Wooden plugs are to be properly cemented in 
the wall or ceiling, and the distance between 
two adjacent plugs should be such that the 
cleats are not more than 60 cm apart 
horizontally or vertically. 

b) Cleats shall be of such dimensions that for 
low voltage installation the distance between 
two wires shall not be less than 2.5 cm centre 
to centre for branch lines and 4 cm for sub- 
main lines. 

c) In no case two wires shall be placed in the 
same groove of the cleats. Also the wires shall 
be laid stretched between the cleats so that 
they do not touch the wall. 

d) Joint cut-outs or fuse cut-outs shall not be used 
in this type of wiring. Where joints become 
unavoidable, wooden junction boxes with 
porcelain connectors inside should be used. 



e) Wiring should be enclosed in a conduit when 
passing through a wall or a floor. The wires 
should run through a conduit upto a height of 
1.5 m level. In case of a metallic conduit, it 
should be properly earthed. Wooden bushings 
are to be provided at both ends of the conduit, 
otherwise insulation of the wires may be 
spoiled when drawn through it. 

f) When two wires cross each other, they should 
be separated by an insulating bridge piece 
which should maintain a distance of atleast 
1.3 cm between the wires. 

g) The wires should not run near water or gas 
pipes or structural work. 

h) A special pattern of cleat may be used where 
conductors pass round corners, so that there 
may be no risk of the conductors touching 
the walls owing to sagging or stretching. 

j) Cleats shall be fixed at distances not greater 
than 60 cm apart and at regular intervals. 

6.1.4 In temporary installations wiring is often done 
over bobbin or knob insulators in place of cleats. 
Whenever the wires pass through a floor or through a 
space where some damage is apprehended, they should 
be provided with an additional protection of a special 
strong covering upto a height of 1 .5 m above the floor 
level. For this purpose, while the wiring passes through 
a wall or a partition, it should be taken inside a tube or 
a pipe or a conduit made of non-inflammable and non- 
hygroscopic material. Porcelain wall-pipe, lead wall- 
tube, iron conduit, etc, are the examples of this type of 
covering. Various components of cleat wiring are 
described below. 

6.1.5 Installation of Cleat Wiring 

6.1,5.1 Cleat wiring is installed along the wall below 
the beam. If there are wooden beams in a house, cleats 
may be directly fixed on the beam for drawing wires 
up to ceiling roses. But if there is an iron beam, then 
space permitting, a piece of wood may be tightly fitted 
on one side of the beam and cleat is fitted on this piece 
of wood. This is shown in Fig. 9. If space is not 
sufficient for fixing a piece of wood on the side of the 




(i) Cleat with two grooves 



d. 



f I 
11 







(ii) Cleat with three grooves 



Fig. 8 Types of Cleat 



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iron beam, at first pieces of wood are clamped at 
intervals to the bottom of the beam and then the cleats 
are fixed on these wood pieces. This is shown in Fig. 10. 
The spacing between two consecutive pieces of wood 
should be such that the wiring must not sag due to its 
own weight. If wiring is to be taken from one room 
into the next, a hole is drilled into the common wall 
and wiring is taken through porcelain or metal tube 
(wall-tube) set into the hole. 




Fig. 9 Cleat is Fixed on an Wood Piece Which is 
Tightly Attached on One Side of an Iron Beam 




SCREW 



ROOF 



HOOP IRON CLAMP FIXED 
WITH WOODEN BEAM BY 
SCREW 



Fig. 10 Arrangement for Drawing Wires 
Under Iron Beam 

If the wires are to be drawn under the iron beam from 
one cleat to the next, arrangements are provided as 
shown in Fig. 1 IB using hoop iron or flat iron clamp. 
For heavy wiring or for lasting and durable job, two 
wrought iron clamps are used as shown in Fig. 1 1 A. 



SET SCREW 



BEAM 




WOOD BELOW 
IRON BEAM 



HOOP IRON CLAMP 

a WIRE 
CLEAT 

Fig. 11 Use of Clamps 

PART 1 GENERAL AND COMMON ASPECTS 



6.1.5.2 Spacing between wires in cleat wiring 

The spacing between wires drawn through the cleats 
depends upon the line voltage, and the type of circuit 
as given at Table 6. An example of cleat wiring system 
is given at Fig. 12. 

Table 6 Spacing of Wires in Cleat Wiring 
(Clause 6.1.5.2 ) 



SI 


Voltage 


Type of 


Centre to Centre 


No. 




Circuit 


Distance Between 
Two Adjacent Wires 


(1) 


(2) 


(3) 


(4) 



i) Not exceeding 250 V 



ii) Exceeding 250 V 



Branch 

Sub-main 

Main 



Not less than 2.5 cm 
Not less than 4 cm 
Not less than 7.0 cm 
10.0 cm distance; 
2.5 cm spacing all 
around 



6.1.5.3 Drawing a wire through wall 

Wall tube or pipe is usually set near the ceiling corner 
(see Fig. 13). The space within the pipe should be 
sufficient to accommodate with comfortable inter- 
space the maximum number of wires to be drawn 
through it. With too many number of wires more than 
one tube may be necessary. In that case pipes are set 
together at one place side by side. Such a tube may be 
made of porcelain or metal. Among metals lead, iron 
or steel is used. The pipe is set inside the wall by means 
of cement. If conduit is used, its two rough ends are 
properly filed and two bushes made of hard wood or 
ebonite are fitted at these ends. This eliminates the 
possibility of damage of the insulation of wires when 
drawn through the pipes. In case of ac wiring all the 
wires must be drawn through the same metal conduit. 
Where wires are drawn outside from a room, the outer 
end of the pipe should be a bit more widened. Also 
this end should have a downward bend so that rain 
water or water from other sources may not get inside 
the pipe along the wires. 

6.1.5.4 Drawing of wires through floors 

If the wires are to be drawn through a hole made in the 
floor, these must be drawn through a conduit pipe upto 
a height of 1 .5 m above the floor level, and the lower 
end of the conduit should be flush with the ceiling 
below. As usual two ends of the conduit must be fitted 
with insulating bushes. 

6.2 Casing Wiring 

In this system of wiring narrow grooved planks of hard 
wood are fixed on wooden plugs grouted in the wall 
instead of cleats and wires drawn along the grooves. 
These narrow planks are called wood casing. Usually 
two long grooves are made in each casing, although 
three-grooved casing is also available. The top of the 



63 



SP 30 : 2011 



LEADS FOR FAN CONNECTION 



JUNCTION BOX 



7 



WIRES DRAWN 
TO NEXT ROOM 




CUT-OUT 

OF CONNECTOR 



5 




CjplEP WIRE FOR FAN 
CONNECTION " 



WIRE FOR LAMP 
CONNECTION 




r 



1.5 METRES ABOVE 
GROUND LEVEL 



r4- 



^> 



.o. 



BRANCH 
LINES 



*\ 



jpL© (pi 



1. SWITCH FOR LAMP 

2. SWITCH FOR FAN 

3. SWITCH FOR 
WALL-PLUG 

4. WALL-PLUG 



Fig. 12 An Example of Cleat Wiring System 





Fig. 13 Use of Wall-tube for Drawing Wires from One Room 
into the Other Through Partition Wall 



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casing is covered by a rectangular strip of wood of the 
same width as that of casing. It is known as capping 
which remains screwed to the casing (see Fig. 14). On 
the surface of the capping a bouble bed is cut to show 
the position of wires so that the screws may not be 
driven through wrong position damaging the insulation 
of the cables laid under the capping. Casing wiring is 
generally adopted for low voltage installations such as 
office and residential buildings. This type of wiring is 
not suitable for places exposed to rain or sun or having 
dampness. It should not also be used in places where 
acids and alkalies are likely to be present. 

6.2.1 The wood used for casing and capping must be 
first class seasoned teak wood or any other hard wood 
free from knots, shakes and saps. The sides should be 
well varnished both inside and outside with pure shellac 
varnish. The size of casing and capping depends upon 
the number of wires drawn through the grooves in a 
particular length of run. 




CAPPING 



CASING 



Fig. 14 Wooden Capping and Casing 

6.2.2 The size of wood casing and capping and number 
of cables that may be drawn in one groove of the casing 
is given in Table 2 of Part 1 /Section 20 of this Code. 

6.2.3 Installation of Casing Wiring 

Casing generally used for installation is about 44 mm 
wide and 16 mm in thickness (height). However, for 
cables of higher sizes, 80-100 mm wide and 
proportionally higher in thickness casings are also in 
use. Casings may be .5.5 m to 6.0 m long, but smaller 
lengths are also available. Lengths of about 2.5 m to 
3.0 m are convenient for handling. Very good 
workmanship is required to make the job perfect, and 
this results in costlier installation. There is also risk of 
fire from wood. 

There are two grooves in each casing. The width of 
the strip of wood separating the two grooves should 
be carefully observed so that it is not less than 13 mm, 
and the portion of wood below each groove shall not 
be less than 7 mm in thickness. In case the cable has a 
large cross-section or a number of cables are to be 
drawn, the size of casing should increase accordingly. 
At the time of wiring the cables laid in the grooves are 
covered by a very thin and long strip of wood which is 
as wide as the casing. This is known as capping. The 



thickness of capping should be about 7 mm. The 
following precautions need to be taken: 

a) Any number of wires of the same polarity may 
be laid in the same groove, but in no case wires 
of opposite polarities are laid in one groove. 

b) Casing should be fixed on dry wall and 
ceiling. Casing shall not be embedded into 
cement or plaster. It shall neither be so set as 
to get contact with a water pipe, nor it shall 
be laid just below a water pipe. It shall not 
also be used in a place where moisture 
accumulates and drips. 

c) A clear space of 3 mm shall be kept between 
wall or ceiling and the casing. This could be by 
means of porcelain insulators (spacing insulator) 
or cleats (either upper half or lower half). 

d) Wooden plugs of approved sizes shall be fixed 
at a distance of 90 cm apart for casing of sizes 
upto 63.5 mm. For higher sizes of casing this 
distance shall not exceed 60 cm. 

e) While passing through floors or walls, heavy 
gauge conduit of approved sizes shall be used . 
The conduit should be securely entered into 
casing, and it should be extended upto a height 
of 1.5 m above floor level. 

f) All joints shall be made with good 
workmanship as per IS 732. 

g) After the wires are laid in the grooves, the 
capping is attached to casing by brass screws 
in a proper way. The screws must not be so 
fixed as to pierce through the insulation of 
the wires. 

h) Capping should be fixed on the casing only 
by screws. The screw used for fixing the casing 
must be long enough to pass through the 
casing, capping, central hole in the bobbin 
insulator or spacing insulator and the wooden 
plug in the wall. The capping is fixed on the 
casing by means of small screws. If the width 
of the casing is less than 50 mm, a series of 
screws are fixed on the central line of the 
capping, and in case the width is more, two 
rows (or columns) of screws are fixed on two 
sides of the capping. For this reason the width 
of the strips of wood on both sides of the casing 
shall not be less than 10 mm. Screws used for 
fixing the capping may be made of brass. 

j) Provision must be there for easy insertion of 
cables into the casing. Before fixing the 
casing, it is necessary to smear its sides and 
back properly with two coats of shellac 
varnish. Further protection is provided by 
painting or varnishing the casing wiring once 
again on all sides after the wiring is finished. 



PART 1 GENERAL AND COMMON ASPECTS 



65 



SP 30: 2011 



k) Spacing insulators may be used at a place 
where the casing is passing below an iron 
beam. Preferred sizes of casings is given in 
Part 1/Section 20. 

6.2.4 Joints in Casing Wiring 

In casing wiring work starts from the farthest point of 
the load circuit, gradually proceeds towards the main 
board and finally ends there. 

a) Joint while fixing lamp — The ceiling rose of 
the lamp bracket is set on a round wooden 
block. This block should have a thickness 
(height) of 4 cm with two coats of varnish 
applied on it. It has a saw-cut on one side in 
such a manner that the tip of the casing closely 
fits on to it {see Fig. 15). 






b) 



FIXED WITH THE 
WOODEN PLUG 
EMBEDDED IN 
THE WALL 



FIXED WITH THE 
WOODEN PLUG 



WIRES COME OUT 
THROUGH THESE TWO 
HOLES AND GO TO 
SWITCH, CELLING ROSE 
OR BRACKET 



Fig. 15 Joint for Fixing Lamp 

Joints for casing/capping — When two pieces 
of casing or of capping are to be joined together, 
the joint should be completed as shown 
in Fig. 16 A (Lap Joint). The joint of capping 
shall be an oblique one {see Fig. 16B), Care 
must be taken to see that cappings are not joined 
together at a point where there is already a joint 
of casing, and also no screw for fixing the 
capping pierces any side wall of the casing. 

1 . Joint at the corner — The kind of joint 
necessary at the corner round is shown 
in Fig. 17. The two tips of casings that 
are to be joined together are placed on 
the floor, cut at an angle of 45° and finally 



16A Joint of Casing 




16B Joint of a Caping with Another 
Caping Out in Oblique 

Fig. 16 Joints for Casing/Capping 

screwed to each other. The corners of the 
grooves should be flush with each other 
so as to prevent any damage to the 
insulation of the cables. The general 
appearance of the joint where the casing 
is taken from one wall to another is at 
Fig. 18 or somewhat similar. The shape 
of such a joint should be such that the 
radius of curvature of the joint should not 
be less than 75 mm so that the insulation 
of cables is not damaged due to twist etc. 
For a corner joints, the piece of casing 
can be abtained as shown in Fig. 19. 



45* 




90° 



45° 



SCREW 



Fig, 17 Joint at a Corner 




CORNER JOINT 
Fig. 18 Shape of Joint at a Corner 



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l\\\\\\\\\\\\\\\\\\\\\\\\s 
7//////////////////////// 

- \\\\\\\\\\\\\\\\\NV\\\\\\ 



Fig. 19 How a Small Piece of Casing is 
Obtained for a Corner Joint 

2) Bending on cables — To bend a VIR or 
PVC cable, the internal radius of bend 
shall be atleast four times the diameter 
of the cable. Where the casing will go 
from one wall to another on the external 
side, the joint should be as per Fig. 20. 



4) 




Fig. 20 Joint of Casing on the External 
Sides of Walls 



3) 



T- Joint — From a point in the continuous 
run of the casing, sometimes connection 
is to be taken out for lamp point, fan 
point, etc, through a joint of the casing, 
known as T- Joint. Where such a joint is 
to be adopted, a V-shaped piece of casing 
is to be cut off upto the middle of the 
casing used in the continuous run. 
Later, the tip of another casing to be 
joined to it is cut off in the shape of V 
and is made flush with the V-groove of 
the former casing as shown in Fig. 21. 




Fig. 21 T- joint 
PART 1 GENERAL AND COMMON ASPECTS 



Bridge — When it is required to draw 
one circuit over another, a small piece of 
casing, named 'bridge', is used so that 
the cable of one circuit does not come in 
touch with that of another. At first the 
bridge is fixed on the casing and then the 
second cable is drawn over it. Where a 
T-joint is necessary, a one-half bridge is 
fixed there along with a full bridge. This 
additional one-half portion is known as 
'half-bridge' . A bridge is also used where 
cable of one circuit crosses that of another 
circuit. Figure 22 depicts 'half bridge' 
and 'bridge'. The joint of casings at this 
point is called 'cross joint'. T-joint and 
cross-joint of casings are shown in 
Fig. 23 and Fig. 24 respectively. 



HALF BRIDGE 




BRIDGE 



Fig. 22 Half Bridge and Bridge 




Fig. 23 T-joint of Casing with Bridges 




Fig. 24 Cross-joint of Casings with Bridge 

6.2.5 Installation of Wiring 

a) Leading a cable from one room to another 
— When leading from one room to another, 
a cable may be drawn either through a casing 
or through a wall-tube. If casing is used, the 
hole in the wall must be large enough to leave 



67 



SP 30 : 2011 



a clearance of at least 25 mm all around the 
casing. The purpose of this clearance is to 
keep the casing dry through ventilation of air. 
If a wall-tube is to be used, the two ends of 
the tube project a little from the wall. The 
partition wall between the grooves at the end 
of casing remaining in contact with the wall- 
tube must be cut off to the same extent as the 
amount of projection of the tube from the wall 
(see Fig. 25). This will keep the wall-tube 
properly fitted with the casing. But in case 
the diameter of the tube is larger than the 
height of the casing or where more than one 
wall-tubes are used, it will not be possible to 
fix the capping over the casing. In such cases, 
the height of the casing is increased with the 
help of a half bridge. 

For continuous earthing system a single 
galvanized iron wire is drawn continuously 
outside the casing along with the cables and 
finally earthed. This is called 'Earth continuity 
conductor'. The outer metallic covers of fan 
regulator iron-clad distribution box, earth 
terminal of the wall socket etc, remain 
connected with this wire. Usually a separate 
wall-tube is used for leading earth continuity 
conductor through the wall. For this work a 
half bridge on the casing near the wall is 
indispensable. 




Fig. 25 Cutting Off a Portion of Casing in Order 
to Fit it with a Wall-tube 

There should be three sockets instead of two 
in every wall socket and three pins instead of 
two with every wall plug. Also the flexible 
cables used in this system must have three 
lengths of insulated wires instead of two. 
b) Leading a cable through the floor — In the 
casing wiring if cables are to be drawn from a 
lower floor to a upper floor, a piece of conduit 
is pushed through a hole made in the floor. 
The sizes of wires of all the circuits to be drawn 
from lower to upper floor are calculated at first, 
and then the size and number of conduits are 
determined accordingly. If continuous earthing 



system is adopted, another extra conduit is to 
be provided for drawing earth continuity 
conductor. At the ceiling of the lower floor all 
conduits must project atleast 25 mm. At both 
ends of a conduit insulating bushes are to be 
fitted. In the upper floor conduit will rise up 
to a height of 1.5 m above the floor level. At 
this end of the conduit one end of a casing 
should remain properly fitted. For proper 
fitting the lower end of the casing is cut to size 
as shown in Fig. 26. If necessary, the spacing 
of the casing from the wall may be increased 
by using a half bridge. Besides, every piece of 
conduit should remain well-earthed. 



INSULATING BUSH 



EARTH WIRE 




HALF-BRIDGE FIXED ON 
CASING 



EARTHING CLAMP FOR 
t CONDUIT 



2.5 

(1 Inch) 



FLOOR 
INSULATING BUSH 



Fig. 26 Leading of Cable Through the Floor 

c) Utility of looping -in- system — Like cleat 
wiring, casing wiring can also be done by 
means of connectors inside junction boxes as 
well as by looping-in-system. Loop wiring has 
many advantages. No joint is necessary and 
the insulation resistance is better retained by 
this system than any other system of wiring. 
The reason for no joint is that, one piece of 
cable is joined with another piece only 
through brass screws of switches and ceiling 
roses. What is meant by jointing of cables does 
not at all happen in this system. Its main 
disadvantage, however, is that the length of 
cable required for wiring is somewhat more. 

6.3 Metal-sheathed Wiring 

6.3.1 The wiring system completed with wires having 
metallic (for example lead) covering over rubber 
insulation is known as 'metal-sheathed' or 'lead- 
covered' wiring. Here the conductors are rubber 
insulated and covered with an outer sheath of lead alloy 
containing about 95 percent lead which provides 



68 



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protection against mechanical injury. Lead sheath 
should be properly earthed. 

6.3.2 The cables may remain exposed to sun or rain, 
but it should not be used where acids and alkalies are 
likely to be present. The cables are laid on wooden 
battens and remain fixed on it by means of brass or 
aluminium link clips spaced at intervals not exceeding 
10 cm horizontally and 15 cm vertically. The thickness 
of the batten should not be less than 10 mm. 

6.3.3 Installation of Metal Sheath 

a) Sharp bends should be avoided. A round bend 
of radius not less than 10 cm may be adopted 
for a change of direction. 

b) Supporting clips used for the cables must not 
set up any chemical reaction with the metal 
sheath. 

c) Lead sheath must be electrically continuous 
and properly earthed. For maintaining 
electrical continuity, bonding of sheaths is 
necessary at joint-boxes and switch boards. 

d) When passing through a floor or crossing a 
wall, the cable must be drawn through 
conduits. Conduits should go up to a height 
of 1.5 m above the floor level. Both ends of 
the conduit should be fitted with ebonite, 
plastic or hard rubber bushings in order to 
protect metal sheath and rubber insulation of 
cables from being damaged. 

6.3.4 Joints for Metal Sheathed Wiring 

a) Connectors — Some special types of 
connector are used for jointing wires or for a 
T-joint to lead a cable to switch board etc. 
These types of connector are more or less the 
same for almost all types of wiring. As per 
requirement two, three or four holes are 
provided in small pieces of porcelain or 
plastic, and inside those holes there are 
connectors in the form of brass tubes. At the 
two ends of the connector there are brass 
screws for fixing the wires. The porcelain or 
plastic portion acts as insulators. When only 
one piece of wire is to be joined with another 
piece, the smallest size connector with a single 
piece of brass tube is used. For jointing twin- 
wire (2-core) from a single cable, a connector 
with two pieces of brass tubes is needed. In 
place of junction cut-outs connector is used 
even in cleat and casing wirings. There are 
holes on the top of all connectors with screws 
to connect wires with the connector (the left 
hand one shows single-joint connector). 
Sometimes the outer cover of a connector is 



made of PVC or bakelite in place of porcelain. 
But as an insulator the use of porcelain is 
better than PVC or bakelite. 
b) Thimbles — Thimble is made of porcelain or 
plastic and looks like a cap as shown in 
Fig. 27. A thimble is threaded inside and it 
becomes pointed towards the upper end. 
Where two or more wires are to be connected 
together, about 6.4 mm of end insulation of 
each wire is taken off and all the ends are then 
twisted together. The combination is then put 
inside a thimble which is turned like a screw 
driver. As a result the thimble pulls the 
combination of twisted ends in by means of 
threads and thus holds it tightly. 




Fig. 27 Wires Connected with Thimble 

c) T- Joint — Where T-connection is taken for a 
point, connectors used there and the mode of 
connection are shown in Fig. 28. A small box, 
called 'joint-box', is used to cover the joint. 
The box may be made of metal or wood. The 
box shall prevent access of insects, dust or 
lime-water (during white washing). The 
advantage of a metal box is that the speciality 
of a lead-sheathed wiring to maintain 
electrical continuity of metal sheath of the 
cables everywhere beginning from the main 
board upto the farthest point of the load circuit 
is automatically retained in it, whereas in case 
of a wooden box it is not so. If a wooden box 
is to be used, an additional bonding clamp 
must be provided in the box and the lead 
sheaths of all the cables taken in for 
connection shall remain fixed with this clamp 
so that electrical continuity is established 
among them. If metal sheath of the cable is to 
be used as an earth continuity conductor, then 
in case of non-metal box, a strip of metal is to 
be used for maintaining continuity of metal 
sheath, and the resistance of such metal strip 
shall be negligible in comparison to that of 



PART 1 GENERAL AND COMMON ASPECTS 



69 



SP 30 : 2011 



the largest size of cable coming into the box 
(see Fig. 29). Joint-box must not be installed 
in a damp place due to possibility of leakage 
of current in the joint-box installed in a damp 
place. Arrangement for maintaining 
continuity between wires near a ceiling rose 
is shown in Fig. 30. In this way, maintaining 
continuity and electrical connections among 
lead sheaths, finally the sheath is connected 
to earth at the main distribution board. If this 
is not done, the insulation of the cable gets 
damaged in a very short time in metal- 
sheathed wiring. If two or more lead-covered 
wires are laid side by side and one wire has 
leakage and its sheath is not well-bonded, 
there will be sparking between them, causing 
damage to the cable. In metal-sheathed 
wiring, electrical continuity of sheath must 
be maintained, and this sheath must not only 
be well-earthed, but the earth connection must 
also be well-maintained. 




Bonding Strip and Unk'ClIp 



Fig. 28 How Wires are Drawn and how These are 
Connected in a T-joint 




wwv 



Tinned UnN Ctfp 

/fy/Yh 



d) 



Fig. 29 Use of Bonding Metal Strip in 
a Wooden Joint-box 
Lead-sheathed cables with earth wire — 
Continuous earthing system ensures safety of 
circuits. According to this system metallic 
covers of table fan, electric iron, electric 
heater, table lamp etc, are to be earthed. In 
case of cleat or casing wiring a single G.I. 
wire is to be drawn as the earth wire along 
with the wiring throughout the house. Use of 



cables having a single earth wire provided 
along with insulated copper wire or wires 
within the same lead sheath can be made. 
While jointing two or more wires, a separate 
connector should also joint all related earth 
wires. If the outer cover and inner lever is 
made of metal, the switch should also be 
earthed as per rule. In such cases lead- 
sheathed cables with earth wire inside is used. 
Connection of earth wire of a circuit with earth 
in the distribution board is shown in Fig. 31. 
Descriptions of different methods and systems 
of wiring (for example cleat or casing wiring) 
are also applicable to metal-sheathed system. 
Looping-in-system of wiring may also be 
adopted with lead-sheathed cables where 
necessary. 




Fig. 30 Maintenance of Continuity 
of Wires Near a Ceiling Rose 




&&:* «M S 



EARTH CONTINUITY BAR 




EARTH WIRE 



Fig. 31 Earth Continuity Bar and Arrangement 

for Connection of Earth Wires 

of Different Circuits 

6.3,5 Installation of Wiring 

a) Drawing of Cables through the Floor — The 
lead-sheathed cable should be drawn through 
a heavy gauze conduit pipe when the cable is 
drawn from lower floor to upper floor. The 
conduit length shall remain extended upto a 



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height of 1.5 m above the floor level in the 
upper floor, while the lower end of the conduit 
shall remain flush with the ceiling of the lower 
floor. Both ends of the conduit should be fitted 
with bushes made of wood or ebonite or some 
other insulating material. 

b) Drawing of cables through partition wall 
between two adjacent rooms — Like other 
systems of wiring metal-sheathed cable 
should also be drawn through porcelain wall- 
tube or steel conduit or hard PVC conduit as 
straight as possible. 

c) Concealed wiring through the wall — Lead- 
sheathed cable cannot be laid direct under 
plaster. For concealed wiring it should be 
either drawn through conduit pipe or by some 
other means after which the whole thing is 
covered with plaster. 

6.4 Cab-Tyre Sheathed (C.T.S.) or Tough Rubber- 
Sheathed (T.R.S.) Wiring 

6.4.0 This type of wiring is adopted only for low voltage 
circuits. C.T.S. wiring is used in open space in place 
of drawing bare conductors. This system of wiring is 
very useful in workshops or places where fumes are 
generated continuously from acids etc, which may 
damage the insulation of ordinary cables or wear out 
conduits etc, or corrode the lead sheath of cables. No 
other insulation is applied on the conductor except hard 
rubber sheath, and in the wiring system cable may not 
be drawn through conduit, casing etc. The advantages 
of this system is that wiring can be done very easily 
and quickly. As a result wiring is economical on the 
whole, although the cable may cost more. C.T.S. wiring 
can be used with a variety of fittings and also in case 
of concealed wiring. The T.R.S. (C.T.S.) system has 
however, now become almost obsolete; as it has been 
replaced by the PVC insulated and sheathed system. 

6.4.1 Installation of C.T.S. Wiring 

When the sheath of C.T.S. cable made of rubber or 
some other compound mixed with rubber remains 
exposed to direct sunlight, arrangement must be 
provided to cover it up properly. It should, however, 
be noted that when sunlight comes through the glass 
of a window, it is not regarded as direct sunlight. Where 
weather proof or lead- sheathed cable is to be drawn 
with the help of catenary wire, either the cable should 
be taken by binding it continuously with the catenary 
wire or it should remain fixed with catenary wire by 
means of link clips at intervals of about 15 cm. C.T.S. 
cable is drawn over the wall in the same way as lead- 
sheathed cable. At first wooden plugs are grouted or 
cemented in the wall at intervals of about 75 cm and 
polished thin batten of teak wood as wide as or a little 



wider than the cable is screwed to these plugs. Tinned 
brass or aluminium link clips are then fixed on this 
batten with the help of iron pins at intervals not 
exceeding 10 cm horizontally and 15 cm vertically. 
For the sake of convenience of work, sometimes clips 
are fixed on the batten at equal intervals in a straight 
line first and then the batten is screwed to the wooden 
plugs. Finally the cable is laid neatly on the clips which 
are then folded. In some cases a batten with clipped 
cable is screwed to the wooden plugs. A single clip 
may be used to fix upto two twin-core, 0.019 4 cm 2 
cables. If the cross- section of the cable is greater than 
this, a single clip may hold only one cable. Where there 
are fumes from acids etc, clips are made of lead strips 
cut out from then lead sheets and iron pins are already 
painted with acid-proof paint. This prevents the iron 
pins being rusted when in contact with acid fumes. 
For a neat and clean look of C.T.S. wiring or for saving 
it from mechanical injury, the wiring may be covered 
by wooden channeling or any other suitable cover. Also 
C.T.S. cables may be drawn through conduit pipes, if 
necessary. During installation of C.T.S. wiring the 
following points are to be kept in mind: 

a) C.T.S. cables should be laid on well seasoned, 
well varnished and perfectly straight hard 
wood of thickness 10 mm and width sufficient 
enough to carry the required number of 
cables. 

b) Wooden batten should remain fixed to rawl 
or phil plugs grouted in the wall or ceiling by 
means of wood screws at an interval not 
exceeding 75 cm. 

c) C.T.S. cables shall never be turned at right 
angles. Wherever there is a bend, the radius 
of curvature shall not be less than six times 
the outer diameter of the cable. While passing 
through wall or floor, cable must be drawn 
through conduit pipes. Metal conduit should 
be properly earthed. 

d) C.T.S. cables shall never be buried under 
plaster. These should be drawn through 
conduit or wooden channeling. 

e) While taking through a floor, the cable shall 
be drawn through a heavy conduit. The two 
ends of the conduit should be fitted with 
bushes made of wood or rubber or any other 
suitable insulating material. The bottom of the 
conduit should be flush with the ceiling of 
the lower floor, while its top must rise upto a 
height of 1.5 m above the floor level of the 
upper floor. Porcelain tubes may also be used 
when the cables are drawn through a wall. 



PART 1 GENERAL AND COMMON ASPECTS 



71 



SP 30: 2011 



6.5 Polyvinyl Chloride (PYC) Sheathed Wiring 

6.5.0 PVC sheathed cable is used extensively in house 
wiring. This cable is available in single-core, twin-core 
or three-core, and its cost is comparatively less than 
that of other wires. PVC cable may be used for wiring 
in open space in place of bare conductor or C.T.S. cable. 
The rubber sheath of C.T.S. cable deteriorates quickly 
in places where there is oil, but PVC insulation is highly 
suitable in such places. PVC insulation can withstand 
acid, alkali, ozone and also direct sunlight. Owing to 
gaps in the sheath it does not dry up, harden and crack 
like rubber. But at higher temperatures PVC softens 
because of which it should not be used at places where 
it is expected to get excessively heated. Also, PVC 
insulation becomes brittle in very cold atmosphere 
therefore it should not be used in places where there is 
ice or snow fall. Wiring systems of PVC wire is similar 
to that of C.T.S. wiring. However, as the PVC wire is 
comparatively lighter than C.T.S. wire, link clips are 
to be fixed on wooden battens at comparatively closer 
intervals. The distance between two adjacent link clips 
should be 6 cm horizontally and 7.5 cm vertically. For 
conduit wiring as well as for concealed wiring, PVC 
cables are drawn through conduit pipes in place of 
V.I.R. wires. The first all-insulated wiring system 
consisted of vulcanized insulated conductors with a 
tough cables sheath (T.R.S.). When first introduced the 
system was known as "cab-type" system (C.T.S.). The 
T.R.S. (C.T.S.) system has now become almost 
obsolete; as it has been replaced by the PVC insulated 
and sheathed system. PVC and similar sheathed cables 
if exposed to direct sunlight shall be of a type resistant 
to damage by ultraviolet light. PVC cable should not 
be exposed to contact with oil, creosote and similar 
hydrocarbons, or should be of a type capable of 
withstanding such exposure. The cables may be 
installed without further protection, except where 
exposed to mechanical damage, in which case they 
must be suitably protected. The all-insulated wiring 
system is used extensively for lighting and socket 
installation in small dwellings, and is one of the most 
economical methods of wiring for this type of work. 
See IS 14772 for joint boxes and IS 371 for ceiling 
roses. An alternative method for wiring with PVC 
sheathed cables for lighting is to use 2-core and circuit 
protective conductor cables with 3 plate ceiling roses 
instead of joint boxes. At the positions of joint boxes, 
switches, sockets and luminaries the sheathing must 
terminate inside the box or enclosure, or could be partly 
enclosed by the building structure if constructed of 
combustible material. 

6.5.1 Installation of PVC Wiring 

a) Bends in Wiring — The wiring shall not in 
any circumstances be bent so as to form a right 



angle but shall be rounded off at the corners 
to a radius not less than six times the overall 
diameter of the cable. 

b) Keeping cables away from pipework — 
Insulated cables must not be allowed to come 
into direct contact with gas pipes or non- 
earthed metal work, and very special care 
must be exercised to ensure they are kept away 
from hot water pipes. 

c) Precautions for cables passing through walls, 
ceiling, etc — Where the cables pass through 
walls, floors, ceilings, partitions, etc, the holes 
shall be made good with incombustible 
material to prevent the spread of fire. It is 
advisable to provide a short length of pipe or 
sleeving suitable bushed at these positions and 
the space left inside the sleeve should be 
plugged with incombustible material. Where 
the cables pass through holes in structural 
steelwork, the holes must be bushed so as to 
prevent abrasion of the cable. Where run 
under wood floors, the cables should be fixed 
to the side of the joists, and if across joists, 
should be threaded through holes drilled 
through the joists in such a position as to avoid 
floorboard nails and screws. In any case, 
screwed 'traps' should be left over all joint 
boxes and other positions where access may 
be necessary. 

d) Fixing cables by suspension on catenary wires 
— Cables can be taken across a lofty building, 
or outside between buildings, if protected 
against direct sunlight by suspending them on 
catenary wires. Galvanized steel wires should 
be strained tight and the cables clipped to the 
wire with wiring clips. Alternatively, they can 
be suspended from the wire with 'rawhide' 
hangers; this provides better insulation 
although not so neat as the former method. 
The catenary wire must be bonded to earth. 

e) Multicore cables have cores of distinctive 
colours, the red should be connected to phase 
terminals, the black to neutral or common 
return and the protective conductor to the 
earth terminal. Clips are much neater than 
saddles, but when more than two cables are 
run together it is generally best to use large 
saddles. If a number of cables have to be run 
together on concrete or otherwise where the 
fixings are difficult to obtain, it is advisable 
to fix a wood batten and then to clip or saddle 
the cables to the batten. Cable runs should be 
planned so as to avoid cables having to cross 
one another, and additional saddles should be 
provided where there is change in directions. 



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PVC sheathed cables should not be used for 
any systems where the normal voltage exceed 
1000 V. 
f) Wiring to socket outlets — When PVC cables 
is used for wiring to socket outlets of other 
outlets demanding an earth connection, it is 
usual to provide 2-core and circuit protective 
conductor cables. These consist of two 
insulated conductors and one uninsulated 
conductor, the whole being enclosed in the 
PVC sheathing. The protective conductor 
shall comply with IS 3043. When wiring to 
16-amps standard domestic sockets, the cable 
will have to be taken into standard box which 
is designed for these sockets and which 
includes an earth terminal. 

6*6 All-Insulated Wiring 

The first all-insulated wiring system consisted of 
vulcanized insulated conductors with a tough cables 
sheath (T.R.S.). The system was initially know as "cab- 
type" system (C.T.S.). The T.R.S. (C.T.S.) system has 
now become almost obsolete; as it has been replaced 
by the PVC insulated and sheathed system. The PVC 
system has many advantages over the old T.R.S. system 
because it is not so inflammable, and will stand up 
better to direct sunlight and chemical action. The cables 
may be installed without further protection, except 
where exposed to mechanical damage, when they must 
be suitably protected. This all-insulated wiring system 
is used extensively for lighting and socket installation 
in small dwellings, and is probably the most 
economical method of wiring for this type of work. It 
is customary to use 2 and 3 -core cables with an integral 
protective or 4-terminal ceiling roses for making the 
necessary connections. 

An alternative method for wiring with PVC sheathed 
cables for lighting is to use 2-core and CPC cables 
with 3 plate ceiling roses instead of joint boxes. 
Terminations of joints in these cables must be enclosed 
in non-ignitable material, such as a box complying with 
IS 14772. 

NOTE — An accessory is a device, other than current using 
equipment associated with such equipment or with the wiring 
of installation. 

At the positions of joint boxes, switches, sockets and 
luminaries the sheathing must terminate inside the box 
or enclosure, or could be partly enclosed by the 
building structure if constructed of combustible 
material. 

6.6.1 Surface Wiring 

When cables are run on the surface, a box is not 
necessary at outlet positions providing the outer 
sheathing is brought into the accessory or luminaries, 



or into a block or recess lined with incombustible 
materials, or into a plastic patress. For vertical-run 
cables which are installed in accessible positions and 
unlikely to be disturbed, support shall be provided at 
the top of the cable, and then at intervals of not less 
than 5 m. For horizontal runs the cables may rest with- 
out fixing in positions which are in accessible and are 
not likely to be disturbed, provided that the surface is 
dry, reasonably smooth and free from sharp edges. For 
cables installed in accessible portions the fixing space 
for cable is 100 to 250 mm for horizontal runs and 
150 to 400 mm for vertical runs. 

Link clips for electrical wiring shall be used for fixing 
the cables installed in accessible positions. Link clips 
shall be so arranged that one single clip shall not hold 
more than two twin-core T.R.S. or PVC-sheathed 
cables up to 1.5 mm 2 above which single clips shall 
hold a single twin-core cable. The clips shall be fixed 
on varnished wood battens with any rust resisting pins 
or screws. For the wiring and runs of mains exposed to 
heat and rain, clip specially made for outdoor use from 
a durable metal, resistant to weather and atmospheric 
corrosion shall be used (see IS 2412 for link clips). 

6.6.2 Concealed Wiring 

PVC wiring, concealed in ceiling partition, is an 
effective method of providing a satisfactory installation 
where appearance is of prime importance as in 
domestic, display or office situations. Where it is 
impractical to run concealed wiring at these locations, 
special precautions are necessary, appropriate 
protection must be provided. This may take the form 
of a cable incorporating an earthed metal sheath, or by 
enclosing the cables in earthed metallic conduit, 
trunking or ducting. PVC sheathed cables shall not be 
buried direct in cement or plaster. The disadvantage is 
that cables once buried in cement or plaster cannot be 
withdrawn should any defect occur. It is better to 
provide a plastic conduit to the switch or outlet 
positions, so that the PVC cables can be drawn into 
the conduit, and withdrawn should the need arise. Such 
an arrangement must also comply with the location 
constraints. Whichever construction is employed, it is 
necessary to provide a box at all light, switch and socket 
outlet position. The boxes must be provided with 
earthing terminals to which the protective conductor 
in the cable must be connected. If the protective 
conductor is a bare wire in multicore cable, a green/ 
yellow sheath must be applied where the cable enters 
the box. 

6.7 Enclosed Wiring System 

6.7.0 Many of the original installations consisted of 
single-core cable supported in cleats. With increasing 
awareness of the possibility of hazard, the necessity 



PART 1 GENERAL AND COMMON ASPECTS 



73 



SP 30 : 2011 



for greater protection created the demand for 
enclosures such as conduit and, later, trunking of which 
there are many different types now available to suit 
different situations. 

6.7.1 Conduit Wiring Systems 

6.7.1.0 Wiring done by insulated wires drawn through 
iron or steel pipes is known as conduit wiring. Conduit 
systems, when assembled in accordance with the 
manufacturer's instructions, shall have adequate 
resistance to external influences according to the 
classification declared by the manufacturers with a 
minimum requirement of IP 30. A conduit system 
which conforms to IS 14930 (Part 1) is deemed safe 
for use. To ensure safety in electrical installations, use 
of metallic conduits as earth continuity conductor is 
not permitted. 

NOTES 

1 Certain conduit systems may also be suitable for use in 
hazardous atmosphere. Regard should be taken for the extra 
requirement necessary for equipment to be installed in such 
condition. 

2 Earthing conductors may or may not be insulated. Earthing 
conductors may or may not be insulated if laid outside, but 
invariably be insulated. 

See IS 14930 (Part 2) for requirements and tests for 
conduit systems buried underground, including 
conduits and conduit fittings for the protection and 
management of insulated conductors and/or cables in 
electrical installations in communication systems and 
IS 9537 (various parts) for conduits. Conduit diameters 



shall be preferably according to Table 7 and points of 
support in accordance with Table 8. Classification 
coding of conduit systems is given at Annex B. 

6.7.1.1 Types of Conduits 

a). Steel conduit system — IS 9537 (Part 2) 
specifies the requirement of rigid steel 
conduits. The screwed steel conduit system 
is used extensively for permanent wiring 
installations, especially for modern 
commercial and industrial buildings (see 
Fig. 32). Its advantages are that it affords the 
conductors good mechanical protection, 
permits easy rewiring when necessary and 
minimizes fire risks. The disadvantages are 
that it is expensive compared with other 
systems, is difficult to install under wood 
floors in houses and flats, and is liable to 
corrosion when subjected to acid, alkali and 
other fumes. Moreover, under certain 
conditions, moisture due to condensation may 
form inside the conduit. Solid drawn conduit 
is much more expensive than welded conduit, 
due to which its use is generally restricted to 
gas-tight and explosion-proof installation 
work. Welded screwed conduit is, therefore, 
generally used for most installation. 

b) Copper conduit — At some places, copper 
conduit is used as it resists corrosion and 
provides excellent continuity. However, the 



Table 7 Outside Diameters — Preferred Values 
(Clause 6.7.1.0) 



SI No. 


Nominal Size 


Outside Diameter 


Tolerance 


Inside Diameter, Min 






mm 


mm 


Mm 


(1) 


(2) 


(3) 


(4) 


(5) 


i) 


25 


25 


+0.5 


18 


ii) 


32 


32 


+0.6 


24 


iii) 


40 


40 


+0.8 


30 


iv) 


50 


50 


+ 1.0 


37 


v) 


63 


63 


+ 1.2 


47 


vi) 


75 


75 


+ 1.4 


56 


vii) 


90 


90 


+ 1.7 


67 


viii) 


110 


110 


+2.0 


82 


ix) 


120 


120 


+2.2 


90 


x) 


125 


125 


+2.3 


94 


xi) 


140 


140 


+2.6 


106 


xii) 


160 


160 


+2.9 


120 


xiii) 


180 


180 


+3.3 


135 


xiv) 


200 


200 


+3.6 


150 


xv) 


225 


225 


+4.1 


170 


yvH 


750 


?50 


+45 


188 



NOTES 

1 Tolerance on outside diameters are given as follows: 

a) Outside diameter specified are nominal dimensions. 

b) Outside diameter maximum is nominal outside diameter + (0,018 x nominal outside diameter values) rounded off to + 0.1 mm. 

c) Minimum inside diameter is nominal outside diameter divided by 1.33. 

2 Any other sizes other than those mentioned in Table 7 shall be as per the agreement between the buyer and the seller. 



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use is limited because the cost could prove to 
be prohibitive. Copper conduit can be screwed 
in the same manner as steel conduit although 
the screwing of copper is more difficult than 
mild steel. Connections are generally made 
by soldering. Bronze junction boxes should 
preferably be used. 



SMOOTH 
BRASS 




32A With Smooth Bore Bush and Coupling 



BRASS 
BUSH 




32B With Brass Ring Bush and Back Nut 

Fig. 32 Methods of Fixing Screwed Conduit at 
Clearance Entries in Metal Casing or Boxes 

c) PVC conduit — When first introduced, such 
conduits had many disadvantages compared 
to steel — the material was mechanically 



weak, greatly affected by changes in 
temperature, did not retain sets, maintained 
combustion (and emitted toxic fumes) and 
tended to separate at joints. These problems 
have now been overcome and, in some 
respects, plastics conduits have many 
advantages over steel. It is much lighter and, 
therefore, easier to handle and install, provides 
a smoother surface for the drawing of the 
cables, is not subject to corrosion and rusting, 
and the super high impact materials now used 
make it suitable for most applications, 
d) Flexible conduit — Several different types of 
flexible conduit are available, ranging from 
convoluted plastics to reinforced corrugated 
steel covered both internally and externally 
with self-extinguishing plastics, the latter 
being the most appropriate for general use. It 
is particularly useful for final connections to 
machinery subject to vibration in place of the 
alternative methods of flexible cable or coiled 
mineral insulated copper cables (MICCs). 
Flexible conduit shall conform to relevant 
Indian Standard. 

6.7*1.2 Cables in conduits 

The types of cables which may be installed in conduits 
are PVC single-core insulated, butyl or silicone rubber 
insulated, with copper or aluminium conductors. PVC 
insulated and sheathed cables are sometimes installed 
in conduits when the extra insulation and protection is 
desirable. Under no circumstances may ordinary 
flexible cords be drawn into conduit. 

6.7.1.3 Selection of correct size of conduit 

After selection of the correct size of cables for a given 
electrical load is made, the selection of the appropriate 
size of conduit to accommodate these cables is to be 
done. The number of cables which may be drawn into 
any conduit must be such that it allows easy drawing 



Table 8 Spacing of Supports for Conduits 

(Clause 6.7.1.0) 



SI No. 


Nominal Size of 
Conduit 






Maximum Distance between Supports 










*r— ' 
















~~~—~*. 






Rigid Metal 




Rigid 


Insulation 




Pliable 








• ■*— 


N 






,-*-, 






~*~ 






*• 




^\ 


*^~~ 




-*\ 






Horizontal 


Vertical 




Horizontal 




Vertical 


Horizontal 


Vertical 






m 


m 




m 




m 


m 




m 


(1) 


(2) 


(3) 


(4) 




(5) 




(6) 


(7) 




(8) 


i) 


Not exceeding 16 


0.75 


1.0 




0.75 




1.0 


0.3 




0.5 


ii) 


Exceeding 16 and not 
exceeding 25 


1.75 


2.0 




1.5 




1.75 


0.4 




0.6 


iii) 


Exceeding 25 and not 
exceeding 40 


2.0 


2.25 




1.75 




2.0 


0.6 




0.8 


iv) 


Exceeding 40 


2.25 


2.5 




2.0 




2.0 


0.8 




1.0 


NOTE 


— A flexible conduit is no 


t normally required to be supported 


in its run. 













PART 1 GENERAL AND COMMON ASPECTS 



75 



SP 30 : 2011 



in, and in no circumstances may it be in excess of the 
maximum given in Part 1/Section 20 of this Code. For 
larger cables it is preferable to install cables in trunking. 
As the number of cables or circuits in a given conduit 
or trunking increase, the current-carrying capacities 
of the cables decrease. Therefore it is advisable not to 
increase the size of the conduit or trunking in order to 
accommodate more cables, but to use two or more 
conduits. The conduit installation must be complete 
before cables are drawn in. This is to ensure that 
subsequent wiring can be carried out just as readily as 
the original. Also the installation must be arranged so 
that cables are not drawn round more than two rigid- 
angle bends. This conduit is complete and ready for 
wiring, and will be concealed when the wall panels 
are fitted. 

6.7.1.4 Conduit system 

There are two distinct conduit systems, the surface 
system, and the concealed system. 

6,7.1.4.1 Surface system 

a) Choice of runs — The most suitable 'run' 
should be chosen for the conduits. When there 
are several conduits running in parallel, they 
must be arranged to avoid crossing at the point 
where they take different directions. The 
routes should be chosen so as to keep the 
conduits as straight as possible, only deviating 
if the fixings are not good. The 'runs' should 
also be kept away from gas and water pipes 
and obstructions which might prove difficult 
to negotiate. Locations where they might 
become exposed to dampness or other adverse 
conditions should be avoided. 

b) Conduit fittings — Bends, inspection tees and 
elbows, made in accordance with relevant 
Indian Standards may be used. However, 
bends can be made by setting the conduit, and 
where there are several conduits running in 
parallel which change direction, it is necessary 
for these bends to be made so that the conduits 
follow each other symmetrically which is not 
possible if manufactured bends are used. The 
use of inspection elbows and tees is not good 
practice, as there is insufficient room for 
drawing in cables and, in addition, the 
installation presents a shoddy appearance. 
Round boxes in accordance with relevant 
Indian Standards may, instead be used. These 
boxes have a much better appearance, provide 
plenty of room for drawing in cables, and can 
accommodate some slack cable which should 
be stowed in all draw-in points. For conduits 
up to 25 mm diameter, the small circular boxes 



should be used. Circular boxes are not suitable 
for conduits larger than 32 mm, and for these 
larger sizes rectangular boxes should be used 
to suit the size of cables to be installed. The 
inspection sleeve is a very useful draw-in 
fitting, because its length permits the easy 
drawing in of cables and its restricted width 
enable conduits to be run in close proximity 
without the need to * set' the conduits at draw- 
in points. Where two or more conduits run in 
parallel, it is a good practice to provide at 
draw-in points an adaptable box which 
embraces all of the conduits. This presents a 
much better appearance than providing 
separate draw-in boxes and has the advantage 
of providing junctions in the conduit system 
which might prove useful if alterations have 
to be made at a later date. Where two or more 
conduits are run in parallel, it is good practice 
to embrace all conduits with an adaptable box 
as shown in Fig. 35. An advantage of the 
conduit system is that the cables can be 
renewed or altered easily at any time. It is, 
therefore, necessary that all draw-in boxes 
should be readily accessible, and subsequently 
nothing should be fixed over or in front of 
them so as to render them inaccessible. The 
need for the conduit system to be complete 
for each circuit, before cables are drawn in, 
is to ensure that subsequent wring can be 
carried out just as readily as the original; it 
prevents cables becoming damaged where 
they protrude from sharp ends of conduit, and 
avoids the possibility of drawing the conduit 
over the cables during the course of erection. 

c) Radius of conduit bends — Facilities such as 
draw-in boxes, must be provided so that cables 
are not drawn round more than two right-angle 
bends or their equivalent. The radius of bends 
must not be less than the standard normal bend 
(see also Fig. 36 and Table 9). 

d) Methods of fixing conduit — There are several 
methods of fixing conduit, and the one chosen 
generally depends upon what the conduit has 
to be fixed to. 

1) Conduit clips — Conduit clips take the 
form a half saddle, and have only one 
fixing lug. The reason for using clips 
instead of saddles is to save an additional 
fixing screw. They are not satisfactory if 
the conduit is subjected to any strain. 

2) Ordinary saddles — Ordinary saddles 
provide a very secure fixing (see Fig. 37). 
They should be fixed by means of two 



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Multiple 
Saddle" 




Two-way through-box 
-Two-way through-box 



Bending of conduit is 
Shown in the diagram 



Conduit Fitting 
Fig. 33 Bending of Conduit 




Right side 
angle box 



Fig. 34 Fittings of Conduits 




NOTE — Where two or more conduits are run in parallel it is good practice to embrace all conduits with an adaptable box. 

Fig. 35 Conduits Run in Parallel 




NOTE — Cable must not be drawn round more than two right angle bends or their equivalent. The four bends in the lower diagram are 
each 45° making a total of 180° in all. 



Fig. 36 Drawing of Cables in Bends 



PART 1 GENERAL AND COMMON ASPECTS 



77 



SP 30 : 2011 



Table 9 Minimum Internal Radii of Bends in Cables for Fixed Wiring 
[Clause 6.7.1.4.1(c)] 



SI No. 



(1) 



Insulation 



(2) 



Finish 



(3) 



Overall Diameter 



(4) 



Factor to be Applied to 

Overall Diameter 1} of Cable 

to Determine Minimum 

Internal Radius of Bend 

(5) 



i) XLPE, PVC or rubber (circular, or 



Non-armoured 



Not exceeding 10 mm 



circular stranded copper or aluminium 
conductors) 



Not exceeding 25 mm 
Exceeding 25 mm 
Armoured Any 

ii) XLPE, PVC or rubber (solid aluminium Armoured or non-armoured Any 

or shaped copper conductors) 
iii) Mineral Copper of aluminium sheath 

with or without PVC overing 



3(2) 2) 
4(3) 2) 
6 
6 



1} For flat cables the factor is to be applied to the major axis. 

2) The figure in brackets relates to single-core circular conductors of stranded construction installed in conduit, ducting or trunking. 



screws and should be spaced not more 
than 1.3 m apart. Nails must not be used 
for fixing (see Fig. 37). The conduit 
boxes to which luminaries are to be fixed 
should be drilled at the back and fixed, 
otherwise a saddle should be provided 
close to each side of the box (see Fig. 38). 




Fig. 37 Spacing Saddles with Oval Holes 




Fig. 38 Saddle 

3) Spacer bar saddles — Spacer bar saddles 
are ordinary saddles mounted on a 
spacing plate. This spacing plate is 
approximately the same thickness as the 
sockets and other conduit fittings and, 
therefore, serves to keep the conduit 
straight where it leaves these fittings as 
well as to prevent the conduit from 



4) 



making intimate contact with damp 
plaster and cement walls and ceilings 
which would result in corrosion of the 
conduit and discoloration of the 
decorations. When conduit is fixed to 
concrete a high percentage of the 
installation time is spent in plugging for 
fixing, and the use of the spacer-bar 
saddle which has only a one-hole fixing 
in its centre has an advantage over the 
ordinary saddle. Some types of spacer bar 
saddles are provided with saddles having 
slots instead of holes. The idea is that the 
small fixing screws need only be loosened 
to enable the saddle to be removed, 
slipped over the conduit and replaced (see 
Fig. 31 and 40). This advantage is offset 
by the fact that when the saddle is fixed 
under tension there is tendency for it to 
slip sideways clear of its fixing screws, 
and there is always a risk of this 
happening during the life of the 
installation if a screw should be come 
slightly loose. For this reason holes rather 
than slots are generally more satisfactory 
in these saddles. When selecting the larger 
sizes of spacer-bar saddles it is important 
to make sure that the slotted hole which 
accommodates the counter-sunk fixing 
screw is properly proportioned. 
Distance saddles — These are designed 
to space conduits approximately 10 mm 
from the wall or ceiling. Distance saddles 
are generally made of malleable cast iron. 
They are much more substantial than other 
types of saddles, and as they space the 
conduit from the fixing surface they 
provide better protection against 



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5) 



corrosion. The use of this type of saddle 
eliminates the possibility of dust and dirt 
collecting behind and near the top of the 
conduit where it is generally inaccessible. 
For this reason distance saddles are usually 
specified for hospitals, kitchens, and other 
situation where dust traps must be avoided. 
Multiple saddles — Where two or more 
conduits follow the same route it is 
generally an advantage to use multiple 
saddles as it saves a considerable amount 
of fixing time because only two screws are 
required, and also all conduits are properly 
and evenly spaced (see Fig. 39 and 42). 




Fig. 39 Multiple Saddle 




Fig. 40 Installation of Conduit 
with Spacing Saddle 







Fig. 41 Multiple Saddle 

6) Girder clips — Where conduits are run 
along or across girders, trusses or other 
steel frame work, standard spring clips 
may be used for be quick and easy fitting. 
Other methods include a range of bolt- 



on devices and if it is intended to run 
number of conduits on a particular route 
and standard clips are not suitable, it may 
be advisable to make these to suit site 
conditions, multiple girder clips can be 
made to take a number of conduits run in 
parallel. As an alternative to girder clips, 
multiple saddles can be welded to 
steelwork, or the steelwork could be 
drilled in case there is no adverse effect 
on its structural properties. 
When conduits are suspended across 
trusses or steel work there is a possibility 
of sagging, especially if luminaries are 
suspended from the conduit between the 
trusses. These conduits should either be 
of sufficient size to prevent sagging, or 
be supported between the trusses. They 
can sometimes be supported by iron rods 
from the roof above (see Fig. 42 and 43). 
If the trusses are spaced 3 mm or more 
apart it is not very satisfactory to attempt 
to run any conduit across them, unless 
there is additional means of support. It is 
far better to take the extra trouble and run 
the conduit at roof level where a firm 
fixing may be found. 




Fig. 42 A U-section Fastened to a Concrete 
Ceiling with Rag-Bolts Used to Carry a 
Number of Saddles of the Required Size 



PART 1 GENERAL AND COMMON ASPECTS 



79 



SF 30: 2011 



e) 



Avoidance of gas, water and other pipes — 
All conduits must be kept clear of gas and 
water pipes, either by spacing or insulation. 
They must also be kept clear of cables and 
pipes which feed telephones, bells and other 
services, unless these are wired to the same 
standard as lighting, heating or power circuits. 
One exemption to this is that conduits may 
be fitted to electrically operated gas valves, 
and the like, if they are constantly under 
electrically skilled supervision. Another is that 
conduits may make contact with water pipes 
if they are intentionally bonded to them. They 
must not make casual contact with water 
pipes. If conduits have to be run near gas or 
water pipes and there is a risk of their making 
contact, they should be spaced apart with 
wood or other insulating material. If the 
conduit system reaches a high potential due 
to defective cables in the conduit and 
ineffective earth continuity, and this conduit 
makes casual contact with a gas or water pipe, 
either of which would be at earth potential, 
then arcing would take place between the 
conduit and the other pipe. This might result 
in puncturing the gas pipe and igniting the 
gas. There is greater likelihood of this 
happening if the gas or water pipe is of lead. 



1 

[ ANGLE 

1 IRON 



TRUSS 



40 X 3mm 
FLAT IRON 
CUP 




Fig. 43 Supporting Several Conduits from 
Angle Iron Truss 

f) Protection of conduits — Although heavy 
gauge conduit affords excellent mechanical 
protection to the cables it encloses, it is 
possible for the conduit itself to become 
damaged if stuck by heavy objects. Such 
damage is liable to occur in workshops where 
the conduit is fixed near the floor level and 
may be struck by trolley or heavy equipment 



being moved or slung into position. Protection 
can be afforded by threading a water pipe over 
the conduit during erection, or by screening 
it with sheet steel or channel iron. Another 
method of protection is, of course, to fix the 
conduit behind the surface of the wall. 




r^-\ 



2> 



NOTE — The conduit is fixed to the ceiling with spacer bar 
saddles. 

Fig. 44 A Supporting Fitting from 
Tangent Tee Box 



TRUSS 



SUPPORT 
FROM ROOF 
TO PREVENT 
SAGGING 



M 




T 



CONDUIT 



STANCHION 



[/ 



Fig. 45 A Conduit Suspended Across 
Roof Trusses 

g) Termination of conduit at switch positions — 
At switch positions the conduit must terminate 
with a metal box or into an accessory or recess 
lined with incombustible material. 



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h) 



Termination of conduit at other than switch 
positions — Where conduit terminates a 
ceiling or wall points other than at switch 
positions, it must terminate with a meal box, 
or recess, or a block of incombustible material. 



WALL 



SURFACE CONDUIT & 
SURFACE SWITCH 




FLUSH CONDUIT & 
FLUSH SWITCH 



NOTE — At switch positions, conduit must terminate with 
metal box or other suitable enclosure. 

Fig. 46 Typical Methods of Terminating Surface 
and Concealed Systems 



t 



CONDUIT 
BOX 



\ 



CONDUIT 
SET OUT 
CLEAR OF 
WALL 



OUTLET 
BOX 



Ci 



METAL 
BOX 



NOTE — A box or suitable enclosure must be fitted at all outlet 
positions. Terminations as shown at B, C and D are not 
permitted. 

Fig. 47 Outlet Positions 

j) Removal of burrs from ends of conduit — 
When steel conduit is cut by a hacksaw, a burr 
is formed upon the inner bore of the conduit. 
If this burr were not removed it would cause 
considerable damage to the insulation of the 
cables drawn into the conduit. Ends of lengths 
of conduit should be free from burrs, and 
where they terminate at boxes, trunking and 
accessories not fitted with spout entries, should 
be treated so as to eliminate damage to cables. 

k) Conduit Installed in damp conditions — If 
metallic conduits are installed externally or in 
damp situations, they should either be 
galvanized, sherardized, or be made of copper, 
and all clips and fixings (including fixing 
screws) shall be of corrosion-resisting material 



m) 



and should be free from burrs. When there is a 
danger of condensation forming inside conduit 
(for example, where there may be changes of 
temperature) suitable precautions should be 
taken. Holes may be drilled at the lowest points 
of the conduit system or, alternatively, conduit 
boxes with drainage holes should be fitted. 
Drainage outlets should be provided where 
condensed water might otherwise collect. 
When ever possible conduit runs should 
designed so as to avoid traps for moisture. 

Continuity of the conduit system — A screwed 
conduit system must be mechanically and 
electrically continuous across all joints so that 
the electrical resistance of the conduit, 
together with the resistance of the earthing 
lead, measured from the earth electrode to any 
position in the conduit system shall be 
sufficiently low so that the earth fault current 
operates the protective device. To achieve this 
it is necessary to ensure that all conduit 
connections are tight and that the enamel is 
removed form adaptable boxes and other 
conduit fittings where screwed entries are not 
provided. To ensure the continuity of the 
protective conductor throughout the life of the 
installation, a separate circuit protective 
conductor is drawn into the conduit for each 
circuit in the conduit._Conduits must always 
be taken direct into distribution boards, 
switchfuses, switches, isolators, starters, 
motor terminal boxes, etc, and must be 
electrically and mechanically continuous 
throughout. Conduits must not be terminated 
with a bush and unprotected cables taken into 




COUPLER AND LOCKNUT 
IN POSITION 



Fig. 48 Connecting Two Lengths of Conduit 

Neither of Which can be Turned, by Use of 

Coupler and Lockout 



PART 1 GENERAL AND COMMON ASPECTS 



81 



SP 30: 2011 



switchgear and other equipment. The 
switchgear must be connected mechanically 
either with solid conduits, or with flexible 
metallic conduits, 
n) Flexible metallic conduit — Flexible metallic 
conduits are used for final connections to 
motors so as to provide for the movement of 
the motor if fixed on slide rails. It also prevents 
any noise or vibration being transmitted from 
the motor, or the machine to which it may be 
coupled, to other parts of the building through 
the conduit system (see Fig. 49). These 
flexible conduits should preferably be of the 
watertight pattern and should be connected 
to the conduit by means of brass adaptors. 
These adaptors are made to screw on to the 
flexible tubing and also into the conduit. It is 
good practice to braze the adaptor to the 
metallic tubing, otherwise it is likely to 
become detached and expose the cables to 
mechanical damage. The use of flexible 
metallic tubing which is covered with PVC 
sleevings is recommended as this outer 
protection prevents oil from causing damage 
to the rubber insertion in the joints of the 
tubing. 




CPC TERMINATES 
WITHIN MOTOR 
CONNECTION BOX 



NOTE — Figure 49A shows the wrong method, which is 
frequently adopted because proper conduit outlets are not 
always provided on starters and motors. The lengths of 
unprotected cable are subject to mechanical damage which may 
lead to electrical breakdown. Figure 49B illustrates the right 
method. Conduit is either taken direct into the equipment or 
terminated with flexible metallic conduit and a suitable c.p.c. 

Fig. 49 Termination Conduit at 
Switch and Starter 

p) Surface conduit feeding luminaires and clocks 
— When surface conduit run to feed wall or 
ceiling accessory like luminaries/clock etc 
which are fixed direct to the wall or ceiling, it 
is advisable, if possible, to set the conduit into 
the wall a short distance from the position of 
the accessory as shown in Fig. 50. 




Fig. 50 Surface Conduit System when Fitting/ 
Accessory must be Flush on Wall or Ceiling 

q) Drawing cables into conduits 

1) Cables must not be drawn in to conduits 
until the conduit system for the circuit 
concerned is complete, except for 
prefabricated flexible conduit systems 
which are not wired in-situ. 

2) When drawing in cables they must first 
of all be run off the reels or drums, or the 
reels must be arranged to revolve freely, 
otherwise if the cables are allowed to 
spiral off the reels they will become 
twisted, and this would cause damage to 
the insulation. If only a limited quantity 
of cable is to be used it may be more 
convenient to dispense it direct from one 
of the boxed reels which are now on the 
market. 

3) Cable must not be allowed to spiral off 
reels or it will become twisted and the 
insulation damaged. 

4) If a number of cables are being drawn 
into conduit at the same time, the cable 
reels should be arranged on a stand or 
support so as to allow them to revolve 
freely. 

5) In new buildings and in damp situations 
the cable should not be drawn into 
conduits until it has been made certain 
that the interiors of the conduits are dry 
and free from moisture. If in doubt, a draw 
wire with a swab at the end should be 
drawn through the conduit so as to 



82 



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remove any moisture that may have 
accumulated due to exposure or building 
operations. 

6) It is usual to commence drawing in cables 
from a mid-point in the conduit system 
so as to minimize the length of cable 
which has to be drawn in. A draw-in tape 
should be used from one draw-in point 
to another and the ends of the cables 
attached. The ends of the cables must be 
bared for a distance of approximately 
50 mm and threaded through a loop in 
the draw tape. When drawing in a number 
of cables they must be fed in very 
carefully at the delivery end whilst some 
one pulls them at the receiving end. 

7) The cables should be fed into the conduit 
in such a manner as to prevent any cables 
crossing, and also to avoid them being 
pulled against the sides of the opening 
of the draw-in box. In hot weather or 
under hot conditions, the drawing-in can 
be assisted by rubbing French chalk on 
the cables. Always leave some slack 
cable in all draw-in boxes and make sure 
that cables are fed into the conduit so as 
not to finish up with twisted cable at the 
draw-in point. 

8) This operation needs care and there must 
be synchronization between the person 
who is feeding and the person who is 
pulling. If in sight of each other this can 
be achieved by a movement of the head, 
and if with in speaking distance by word 
of command given by person feeding the 
cables. If the two persons are not with in 
earshot, then the process is somewhat 
more difficult. A good plan is for the 
individual feeding the cables to give pre- 
arranged signals by tapping the conduit 
with a pair of pliers. 

9) In some cases, it may be necessary for a 
third person to be stationed midway 
between the tow positions to relay the 
necessary instructions from the person 
feeding to the person pulling. Otherwise 
cables may become crossed and this 
might result in the cables becoming 
jammed inside the conduit. 

10) The number of cables drawn into a 
particular size conduit should be such that 
no damage is caused to either the cables 
or to their enclosure during installation. 
It will be necessary, after deciding the 
number and size of cables to be placed 



in a particular conduit run, to determine 
the size of conduit to be used. Each cable 
and conduit size is allocated a factor and 
by summing the factors for all the cables 
to be run in a conduit route, the 
appropriate conduit size to use can be 
determined. 

6.7.1.4.2 Concealed conduit system 

6.7.1.4.2.1 Screwed metal conduit is particularly 
suitable for concealed wiring. The conduit can be 
installed during building operations and can be safely 
buried in floors and walls whether the floors or walls 
are constructed of wood, brick, hollow tiles or solid 
concrete, in such a manner that the cables can be drawn 
in at any time after the completion of the building. The 
conduit system, if property installed, can be relied upon 
adequately to protect the cables and allows them to be 
replaced at any time if desired. Most modern buildings, 
including blocks of flats, are constructed with solid 
floors and solid walls and it is necessary for the conduit 
(if concealed) to be erected during the construction of 
the building. In other types of building where there 
are wooden joists and plaster ceilings, conduit will have 
to be run between and across the joists. 



a) 



Running conduit in wooden floors — Where 
conduit is run across the joists, they will have 
to be slotted to enable the conduit to be kept 
below the level of the floor boards. When slots 
are cut in wooden joists they must be kept as 
near as possible to the bearings supporting 
the joists, and the slots should not be deeper 
than absolutely necessary, otherwise the joists 
will be unduly weakened {see Fig. 51). The 
slots should be arranged so as to be in the 
centre of any floorboards, if they are near the 
edge there is the possibility of nails being 
driven through the conduit. The slots cut in 
the joists should be no deeper than necessary 
and kept as near as possible to the bearing of 
the joints so as not to weaken them unduly. 
'Traps' should be left at the position of all 
junction boxes. These traps should consist of 
a short length of floor board, screwed down 
and suitably marked. 



FLOOR BOARDS 




Fig. 51 Running Conduit in Wood Floors to Feed 
Lighting Points 



PART 1 GENERAL AND COMMON ASPECTS 



83 



SP 30: 2011 



b) Running conduits in solid floors — Where c) 

there are solid floors, it is impossible to leave 
junction boxes in the floors, unless there is a 
cavity above the top of the floor slab, in which 
case the conduits may be run in the cavity 
and inspection boxes arranged so as to be 
accessible below the floor boards. Otherwise 
the conduit needs to be arranged so that cables 
can be drawn in through ceiling or wall points. 
This methods is known as the' looping-in 
system' , and it is shown in Fig. 52 and Fig. 53 
and conduit boxes are provided with holes at 
the back to enable the conduit to be looped 
from one box to another. These boxes are 
made with two, three or four holes so that it 
is possible also to tee off to switches and 
adjacent ceiling or wall points. If the floors 
are of reinforced concrete, it may be necessary 
to erect the conduit system on the shuttering 
and to secure it in position before the concrete 
is poured. Wherever conduit is to be buried 
by concrete, special care must be taken to d) 

ensure that all joints are tight, otherwise liquid 
cement may enter the conduit and form a solid 
block inside. Preferably the joints should be 
painted with bitumastic paint, and the conduit 
itself should also be painted where the enamel 
has been removed during threading of setting. 
Sometimes the conduits can be run in chases 
cut into concrete floors; these should be 
arranged so as to avoid traps in the conduit 
where condensation may collect and damage 
the cables. 



Conduit runs to outlets in walls — Sockets 
near skirting level should preferably be fed 
from the floor above rather than the floor 
below, because in the latter case it would be 
difficult to avoid traps in the conduit (Fig. 54), 
When the conduit is run to switch and other 
positions in walls it is usually run in a chases 
in the wall. These chases must be deep 
enough to allow at least 10 mm of cement 
and plaster covering; otherwise rust from the 
conduit may come through to the surface. 
Conduits buried in plaster should be given a 
coat of protective paint, or should be 
galvanised. The plaster should be finished 
neatly round the outside edges of flush switch 
and socket boxes, otherwise the cover plates 
may not conceal any deficiencies in the 
plaster finish. When installing flush boxes 
before plastering, it is advisable to stuff the 
boxes with paper to prevent their being filled 
with plaster. 

Ceiling points — At ceiling points the conduit 
boxes will be flush with the finish of the 
concrete ceiling. If the ceiling is to have a 
plaster rendering, this will leave the front of 
the boxes recessed above the plaster finish. 
To overcome this it is possible to use extension 
rings for standard conduit boxes. At the 
position of ceiling points pit is usual top 
provide a standard found conduit box, with 
an earth terminal, but any metal box or 
incombustible enclosure may be used, 
although an earth terminal must be provided. 




-NUMBERS INDICATE NUMBER OF CABLES IN THE 
CONDUITS 



Fig. 52 Typical Arrangement of Concealed Conduits Feeding Lighting Points by Looping the Conduit 

into the Back of Outlet Boxes 



84 



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///^///MMMK^^^mm////M 




Fig. 53 Details of Conduit Box and Method of Hastening Conduit 



WRONG 
METHOD 



SOCKET OUTLET 
BOXES 



FLOOR 



fazZZa2Z3%?7^ 







CORRECT METHOD 




LOOPING BOXES 



SOCKET OUTLET 
BOXES 



CEILING 



FLOOR 



NOTE — If the sockets are fed from the floor below, it is difficult to avoid a trap for moisture. 

Fig. 54 Right and Wrong Methods of Feeding Socket Near Skirting Level 



e) Running sunk conduits to surface distribution 
boards — Where surface mounted 
distribution boards are used with a sunk 
conduit, the problems arises as to the best 
method of terminating flush conduits into the 
surface boards. One method is to 'set' the 
conduits out to the required distance into the 
surface boards but this is not recommended. 
A better method is to fit a flush adaptable box 



in the wall behind the distribution board and 
to take the flush conduits directly into it. Holes 
can be drilled in the back of the distribution 
board and bushed. Spare holes should be 
provided for future conduits. Alternatively, an 
adaptable box can be fitted at the top of the 
distribution board, partly sunk into the wall 
to receive the flush conduits, and partly on 
the surface to bolt on the top of the distribution 



PART 1 GENERAL AND COMMON ASPECTS 



85 



SP 30 : 2011 



board. Distribution boards must be bonded to 
the adaptable boxes. 

f) Before wiring sunk conduit - — Before wiring, 
the conduits for each circuit must be erected 
complete. Not only should they be complete 
but they must be clean and dry inside 
otherwise the cables may suffer damage. No 
attempt should be made to wire conduits 
which are buried in cement until the building 
has dried out and then the conduits should be 
swabbed to remove any moisture or 
obstruction which may have entered them. 

g) The light mechanical stress unscrewed conduit 
system — The light mechanical stress conduit 
system consists of conduits, the walls of which 
are not of sufficient thickness to allow them 
to be threaded. Instead of screwed sockets and 
fittings grip type fittings are used. 

h) Insulated conduit system — Non-metallic 
conduits are now being increasingly used for 
all types of installation work, both for 
commercial and house wiring. The PVC rigid 
conduit is made in various sizes and there are 
various types of conduit fittings, including 
boxes available for use with this conduit. The 
type of universal conduit box is made of a 
plastic material, and fitted with special 
sockets, and enable the conduit to be merely 
slipped into position, and secured by locking 
ring. No cement is required, except that it is 
recommended in damp situations. The 
advantage of the insulated conduit system is 
that it can be installed much more quickly than 
steel conduit, it is non-corrosive, impervious 
to most chemicals, weatherproof, and it will 
not support combustion. The disadvantages 
are that it is not suitable for temperatures 
below -5°C or above 60°C, and where 
luminaries are suspended from PVC conduit 
boxes, precautions must be taken to ensure 
that the heat from the lamp does not result in 
the PVC box reaching a temperature 
exceeding 60°C. For surface installations it is 
recommended that saddles be fitted at 
intervals of 800 mm for 20 mm diameter 
conduit, and intervals of 1 600 mm to 
2 000 mm for larger sizes. The special sockets 
and saddles for this type of conduit must have 
provision to allow for longitudinal expansion 
that may take place with variations in ambient 
temperature. It is necessary to provide a circuit 
protective conductor in all insulated conduit, 
and this must be connected to the earth 
terminal in all boxes for switches, sockets and 
luminaries. The only exception is in 



connection with Class 2 equipment, that is, 
equipment having double insulation. In this 
case a protective conductor must not be 
provided. Flexible PVC conduits are also 
available, and these can be used with 
advantage where there are awkward bends, 
or under floorboards where rigid conduits 
would be difficult to install. 

6.7.1.4.2.2 Installation of plastic conduit 

Plastic conduits and fittings can be obtained from a 
number of different manufacturers and the techniques 
needed to install these are not difficult to apply. Care 
is however needed to assemble a neat installation and 
the points given below should be borne in mind. As 
with any other installation good workmanship and the 
use of good quality materials is essential. 

It should be noted that the thermal expansion of plastic 
conduit is about six times that of steel, and so whenever 
surface installation of straight runs exceeding 6 m is 
to be employed, some arrangement must be made for 
expansion. The saddles used have clearance to allow 
the conduit to expand. Joints should be made with an 
expansion coupler, which is attached with solvent 
cement to one of the lengths of tube, but allowed to 
move in the other. 

Cutting the conduit can be carried out with a fine tooth 
saw or using the special tool. As with steel conduit, it 
is necessary to remove any burrs and roughness at the 
end of the cut length. 

Bending the small sizes of plastic conduit up to 25 mm 
diameter can be carried out cold, A bending spring is 
inserted so as to retain the cross sectional shape of 
the tube. It is important to use the correct size of 
bending spring for the type of tube being employed. 
With cold bending, the tube should initially be bent 
to about double the required angle, and then returned 
to the angle required, as this reduces the tendency of 
the tube to return to its straight form. To bend larger 
sizes of tube, 32 mm diameter and above, judicious 
application of heat is needed. This may be applied by 
blowlamp, electric fire or boiling water. If a naked 
flame is used, extreme care must be taken to avoid 
overheating the conduit. Once warm, insert a bending 
spring and bend the tube round a suitable former. A 
bucket is suitable, but do not use a bending machine 
former, as this conduits away the heat too rapidly. The 
formed tube should as soon as possible be saddled 
after bending. 

Joints are made using solvent adhesives, which can be 
obtained specifically for the purpose. These adhesives 
are usually highly flammable and care is needed in 
handling and use. Good ventilation is essential, and it 



86 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



is important not to inhale any fumes given off. The 
manufacturers' instructions for use of the solvent 
adhesive should be strictly followed. If sealing is 
needed to waterproof the joint, use a special non-setting 
adhesive or grease. Threaded adaptors are available 
for use when it is required. Drawing in cables is carried 
out by making use of a nylon draw-in tape. The smooth 
bore of the plastic tube aids the pulling in operation. 
Liquid soap or French chalk maybe used to provide 
lubrication to help the pulling in process. Capacities 
of plastic conduits maybe calculated in a similar way 
to that used for steel systems. Each type of cable is 
allocated a factor, and corresponding factors are 
allocated for various sizes of conduit. Table 10 and 
Table 1 1 give the factors applicable to cables and 
conduits. This requires that when cables are drawn into 
conduit damage to both cables and conduit is avoided. 
The use of plastic conduit is suitable when cable runs 
require to be located in pre-cast concrete. As will be 
appreciated it is essential that sound joints are made 
so that when the concrete is cast, the conduit runs do 
not separate. The maximum permissible number of 
1 . 1 kV grade cables that can be drawn into rigid steel 
conduits are given at Table 3 of Part 1 /Section 20 of 
this Code. The maximum permissible number of 
1 . 1 kV grade single-core cables that may be drawn into 
rigid non-metallic conduits are given in Table 4 of 
Part 1/Section 20 of this Code. Table 1 of Part 1/ 
Section 20 gives diameter and maximum allowable 
resistance of fusewires of tinned copper. 

6.7*2 Cable Trunking and Ducting Systems 

6.7.2.0 General 

Cable trunking and cable ducting systems are used for 
the accommodation, and where necessary for the 
segregation of conductors, cables or cords and/or other 
electrical equipment in electrical installations 
{see Fig. 55). The systems are mounted directly on walls 
or ceilings , flush or semi-flush or indirectly on walls or 
ceilings, or on structures away from on walls or ceilings. 
See IS 14927 (Part 1) for general requirements of the 
cable trunking and ducting systems. For general use, 
cable trunking is now available in various materials such 
as steel, PVC, aluminium and phenylene oxide (Noryl), 
in a wide range of sizes of both square and rectangular 
cross-section. Steel cable trunking is supplied in various 
standard lengths with provision for slotting together and 
bolting to maintain electrical continuity for bonding. If 
required, trunking is available with pin supports at 
regular intervals for separating circuits and, where it is 
essential to completely segregate wiring, such as safety 
services and extra-low voltage, continuous barriers are 
provided. 

Where a large number of cables has to be run together, 
it is often convenient to put them in trunking. Trunking 



for electrical purposes is generally made of 1.2 mm 
sheet steel, and is available is size ranging from 50 mm 
x 50 mm to 600 mm x 150 mm, common sizes being 
50 mm x 50 mm, 75 mm x 100 mm, 150 mm x 75 mm 
and 150 mm x 150 mm although 50 mm x 100 mm 
and 100 mm x 100 mm are also available. See Table 
12 for spacing of supports for trunking and Table 13 
for preferred dimensions of cable trunking and 
ducting. 

6.7.2.1 Types of trunking 

a) Metallic trunking — Trunking for industrial 
and commercial installations is often used in 
place of the larger sizes of conduit. It can be 
used with advantage in conjunction with 16 
mm to 32 mm conduits, the trunking forming 
the background or framework of the system 
with conduits running from the trunking to 
lighting or socket outlet points. For example, 
in a large office building, trunking can be run 
above the suspended ceiling along the 
corridors to feed corridor points, and rooms 
on either side can be fed from this trunking 
by conduit. 

In multistorey ed buildings trunking of suitable 
capacity, and with the necessary number of 
compartments, is to be provided and run 
vertically in the riser ducts and connected to 
distribution boards; it can also accommodate 
circuit wiring, control wiring, also cables 
feeding fire alarms, telephones, emergency 
lighting and other services associated with a 
modern building. 

Cables feeding fire alarms and emergency 
circuits need to be segregated by fire-resisting 
barriers from those feeding low-voltage 
circuits (that is 50 V to 1 000 V ac). It is usual 
for telecommunications companies to insist 
that their cables are completely segregated 
from all other wiring systems. It may therefore 
be necessary to install 3 or 4 compartment 
trunking to ensure the requirements for data 
and telecommunications circuits are complied 
with. Cables feeing emergency lighting and 
fire alarm must also be segregated from the 
wiring of any other circuits by means of rigid 
and continuous partitions of non-combustible 
material. 

b) Non-metallic trunking — A number of 
versatile plastic trunking systems have been 
developed in recent years and these are often 
suitable for installation work in domestic or 
commercial premises, particularly where 
rewiring of existing buildings is required. 



PART 1 GENERAL AND COMMON ASPECTS 



87 



§§ Table 10 Conduit Factors for Runs Incorporating Bends Eg 

(Clause 6.7.1.4.2.2) g 

o 



2 

8 
> 

w 

w 
n 

H 

s 

> 

r 

o 



SI No. 


Length of Run 

m 

(2) 




Straight 






One Bend 






Two Bends 






Three Bends 






Four Bends 




(1) 


16 

(3) 


20 
(4) 


25 
(5) 


32 
(6) 


16 
(7) 


20 
(8) 


25 
(9) 


32 
(10) 


16 
(11) 


20 
(12) 


25 
(13) 


32 
(14) 


16 
(15) 


20 
(16) 


25 
(17) 


32 
(18) 


16 
(19) 


20 
(20) 


25 
(21) 


32 
(22) 


i) 


1 










188 


303 


543 


947 


177 


286 


514 


900 


158 


256 


463 


818 


130 


213 


388 


692 


ii) 


1.5 










182 


294 


528 


923 


167 


270 


487 


857 


143 


233 


422 


750 


111 


182 


333 


600 


iii) 


2 










177 


286 


514 


900 


158 


256 


463 


818 


130 


213 


388 


692 


97 


159 


292 


529 


iv) 


2.5 










171 


278 


500 


878 


150 


244 


442 


783 


120 


196 


358 


643 


86 


141 


260 


474 


v) 


3 










167 


270 


487 


857 


143 


233 


422 


750 


111 


182 


333 


600 










vi) 


3.5 


179 


290 


521 


911 


162 


263 


475 


837 


136 


222 


404 


720 


103 


169 


311 


563 










vii) 


4 


177 


286 


514 


900 


158 


256 


463 


818 


130 


213 


388 


692 


97 


159 


292 


529 










viii) 


4.5 


174 


282 


507 


889 


154 


250 


452 


800 


125 


204 


373 


667 


91 


149 


275 


500 










ix) 


5 


171 


278 


500 


878 


150 


244 


442 


783 


120 


196 


358 


643 


86 


141 


260 


474 










x) 


6 


167 


270 


487 


857 


143 


233 


422 


750 


111 


182 


333 


600 


















xi) 


7 


162 


263 


475 


837 


136 


222 


404 


720 


103 


169 


311 


563 


















xii) 


8 


158 


256 


463 


818 


130 


213 


388 


692 


97 


159 


292 


529 


















xiii) 


9 


154 


250 


452 


800 


125 


204 


373 


667 


91 


149 


275 


500 


















xiv) 


10 


150 


244 


442 


783 


120 


196 


358 


643 


86 


141 


260 


474 



















SP 30 : 2011 



Recessed screw 



Locking bar 




Gusset bend 



Gusset tee 



Elbow bend 



Fig. 55 Cable Trunking 



Table 11 Cable Factors for Long Straight Runs, 

or Runs Incorporating Bends in Conduit 

(Clause 6.7.1.4.2.2) 



Type of Conductor 


Conductor, Cross- 
Sectional Area 


Factor 




1.0 


16 


Solid or stranded 


1.5 


22 




2.5 


30 




4.0 


43 




6.0 


58 




10.0 


105 



c) Mini trunking — For domestic or similar small 
installations, mini-trunking systems similar in 
form to cable trunking but of less obstructive 
cross-section, ranging from 16 mm to 75 mm 
wide by 12 mm to 30 mm deep can be used. 
There are numerous accessories for bends, 
junctions and outlets and, with the exception 
of the outlets which are usually surface 
mounted. A complete installation can be made 
quite inconspicuously by close fitting to 
skirtings, picture rails and door architraves. 
Because of the small section, runs on walls or 
across ceilings can be used without spoiling the 
aesthetics of an area. 



Mini-trunking and cove-trunking are 
particularly suitable for areas which may be 
subject to changes of layouts, or for rewiring, 
to avoid major unheavals in addition to new 
installations. The simplicity of installations 
and the degree of accessibility provided by 
these systems can reduce labour costs 
tremendously. 

d) Lighting trunking system — Steel or alloy 
lighting trunking was originally designed to 
span trusses other supports in order to provide 
an easy an economical method of supporting 
luminaries in industrial premises at high level. 

e) Underfloor trunking system/Floor distribution 
system — Open plan office and other types of 
commercial buildings may well need power 
and data wiring to outlets at various points in 
the floor area. The most appropriate way of 
providing this is by one of the underfloor 
wiring systems now available. Both steel and 
plastic construction trunking can be obtained, 
and if required 'power poles' can be inserted 
at appropriate locations to bring the socket 
outlets to a convenient hand height. With the 
increasing use being made of computers, and 



Table 12 Spacing of Supports for Trunking 
(Clause 6.7.2.0) 



SI No. 



(1) 



Cross-sectional Area, mm 2 



(2) 



Maximum Distance Between Supports 





*-— * 










-x 






Metal 








Insulating 






^*^ 








-^ 






r- 




*-\ 


/"*■" 










Horizontal 




Vertical 


Horizontal 






Vertical 


m 




m 




m 






m 


(3) 




(4) 




(5) 






(6) 


0.75 




1.0 




0.5 






0.5 


1.25 




1.5 




0.5 






0.5 


1.75 




2.0 




1.25 






1.25 


3.0 




3.0 




1.5 






2.0 


3.0 




3.0 




1.75 






2.0 



i) Exceeding 300 and not exceeding 700 

ii) Exceeding 700 and not exceeding 1 500 

iii) Exceeding 1 500 and not exceeding 2 500 

iv) Exceeding 2 500 and not exceeding 5 000 

v) Exceeding 5 000 



PART 1 GENERAL AND COMMON ASPECTS 



89 



SP 30 : 2011 



other electronic data transmission systems, the 
flexibility of the underfloor wiring can be 
used to good advantage. 

f) Steel floor trunking — Under floor trunking 
made of steel is used extensively in commercial 
and similar buildings, and it can be obtained 
in very shallow sections with depth of only 
22 mm, which is very useful where the 
thickness of the floor screed is limited. 

g) Plastic underfloor trunking — Plastic 
materials are now often used instead of their 
metal counterparts for the enclosures of 
underfloor systems. Under floor trunking 
systems made with this material can be 
divided into two main types, these being 
raised floor systems and underfloor systems. 

h) Carpet trunking system — A carpet trunking 
is provided for fixing to a finished floor, which 
has a total depth of 9.6 mm. It is complete 
with a snap on overlapping lid which, when 
it place, forms a retainer for abutting carpet. 

NOTE — There are many different designs, the 
particular requirements of which are covered in other 
parts of IS 14927. 

6.7.2.2 Trunking and ducting systems shall be so 
designed and constructed that where required they 
ensure reliable mechanical protection to the conductors 
and/or cables contained therein. Where required, the 
system shall also provide adequate electrical protection. 
In addition, the system components shall withstand the 
stresses likely to occur during transport, storage, 
recommended installation practice and usage. System 
Components are parts used within the system, which 
include lengths of trunking or ducting, trunking or 
ducting fittings, fixing devices, apparatus mounting 
devices, and other accessories. 

NOTE — The above mentioned components may not 
necessarily be included all together in a system. Different 
combinations of components may be used. 



In addition, for cable trunking and ducting systems 
intended for mounting on walls or ceilings, the 
manufacturer's instruction on classification of the CT/ 
DS and on installation of the system should be 
followed. If the system is intended for the suspension 
of loads, the manufacturers on the maximum load and 
method of suspension should be followed. 

The sizes of the cable trunking and ducting other than 
those specified are also acceptable as per the agreement 
between the purchasers and the manufacturers provided 
that the height and width are from the combination of 
the following dimensions having tolerances of ±0.2 
mm on both height and width dimensions. 12 mm, 
16 mm, 20 mm, 25 mm, 32 mm, 38 mm, 50 mm, 
75 mm and 100 mm. 

Wall thickness for cable trunking and ducting for any 
type of combination with respect to height and width 
as given in clause shall be as follows: 

a) Any combination where size is up to 32 mm 
the wall thickness shall be at least 1.20 mm. 

b) Any combination where size is up to 38 mm, 
the wall thickness shall be at least 1.30 mm. 

c) Any combination where size is up to 50 mm 
the wall thickness shall be atleast .1.50 mm. 

d) Any combination where size is above 50 mm 
the wall thickness shall be at least 1.80 mm. 

6.7.2.3 Access to live parts 

Trunking/ducting systems shall be so designed that 
when they are installed and fitted with insulated 
conductors and apparatus in normal use, parts are not 
accessible. 

6.7.2.4 Designs of conduit system 

A schematic of trunking and ducting systems for wall, 
ceiling installation and floor installation is given at 
Fig. 56. 



Table 13 Preferred Dimensions of Cable Trunking and Ducting 
{Clause 6.7.2.0 ) 



Size 


Approximate Internal Cross- 


Outer 


Outer 


Wall Thickness 




Sectional 


Width 


Height 


Min 


mm 


mm 2 


mm 


mm 


mm 


(1) 


(2) 


(3) 


(4) 


(5) 



12x12 


119.50 


12.0 ± 0.2 


12.0 ± 0.2 


16x12 


153.00 


16.0 ± 0.2 


12.0 ± 0.2 


16x16 


196.00 


16.0 ± 0.2 


16.0 ± 0.2 


25 x 12 


239.10 


25.0+ 0.2 


12.0 + 0.2 


25x16 


307.40 


25.0+ 0.2 


16.0 + 0.2 


25 x 25 


510.80 






38x16 


474.40 


25.0±0.2 


25.0 ± 0.2 


38x25 


793.00 


38.0 ± 0.2 


16.0 ± 0.2 


50x16 


611.00 


38.0 ± 0.2 


25.0 + 0.2 


50x50 


2 209.00 


50.0 ± 0.2 


16.0 ±0.2 


75x75 


5 098.00 


50.0 ± 0.2 


50.0 ± 0.2 


100x50 


4 473.00 


75.0+ 0.2 


75.0 ± 0.2 






100.0 ± 0.2 


50.0 ± 0.2 



1.20 
1.20 
1.20 
1.20 
1.20 
1.20 
1.30 
1.30 
1.50 
1.50 
1.80 
1.80 



90 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



CD 






© o 



/ 



® 



«® 






(D 



<(D 



«<D 




^3L 



© 



n 



i ii i 

11 Ef 



NOTE — No. 5 represents an apparatus in a trunking system. 



a) Types and Application of Trunking and Ducting System for Wall and Ceiling Installation 



No. on 
Fig. 56 

0) 



Definition 

(2) 



For 

(3) 



Counting 
(4) 



1 
7 
11 
12 
13 
15 

3 
9 



2 

10 
8 



Trunking and 
accessories 



Trunking and 
accessories 

Trunking and 
accessories 



Ducting and 
accessories 



Ducting and 
accessories 



Insulated conductors, cables, Surface on wall and ceiling, on walls 
cords mounted horizontally or vertically, ceiling 

suspended 



Insulated conductors, cables, Flush in wall and ceiling, in walls mounted 

cords horizontally or vertically 

Insulated conductors, cables, Surface on wall and ceiling, on walls 

cords, mounting devices for mounted horizontally or vertically 
apparatus (switches, socket- 
outlets, circuit-breakers, etc 

Insulated conductors, cables, Surface on wall and ceiling, on walls 

cords mounted horizontally or vertically, ceiling 

suspended 



Insulated conductors, cables, 
cords 



Embedded in wall and ceiling, in walls 
mounted horizontally or vertically 



PART 1 GENERAL AND COMMON ASPECTS 



91 



SP 30 : 2011 



b) Trunking and Ducting Systems for Floor Installation 



No. on 
Fig. 56 

(1) 



Definition 

(2) 



For 

(3) 



Mounting 

(4) 



3 

7 



Trunking and accessories 
Trunking and accessories 

Ducting and accessories 

Ducting and accessories 
Electrical service unit 

Electrical service unit 
Skirting systems 



Insulated conductors, cables, cords Flush floor 

Insulated conductors, cables, cords Surface on floor 

Insulated conductors, cables, cords, Flush floor 

Insulated conductors, cables, cords In floor (embedded) 

Apparatus Flush floor 



Apparatus 



Surface on floor 



6 

15 
Not shown 



Skirting trunking and accessories Insulated conductors, cables, cords Surface on wall and ceiling 

Skirting trunking and accessories Insulated conductors, cables, cords, Surface on wall and ceiling 

counting devices for apparatus 



Not shown Socket plinth 



Mounting apparatus (socket-outlets) Surface on wall 



Fig. 56 Types of Trunking and Ducting Systems 



7 EQUIPMENT, FITTINGS AND ACCESSORIES 

7,0 An important stage of electrical installation work 
is the fixing of accessories, such as ceiling roses, 
holders, switches, socket outlets and luminaries. This 
work requires experience and a thorough knowledge 
of the regulations which are applicable, because 
danger from shock frequently results from the use of 
incorrect accessories or accessories being wrongly 
connected. 

All equipment shall be suitable for the maximum power 
demanded by the current using equipment when it is 
functioning in its intended manner. In wiring other than 
conduit wiring, all ceiling roses, brackets, pendants and 
accessories attached to walls or ceilings shall be 
mounted on substantial teak wood blocks twice 
varnished after all fixing holes are made in them. 
Blocks shall not be less than 4 cm deep. Brass screws 
shall be used for attaching fittings and accessories to 
their base blocks. Where teak or hardwood boards are 
used for mounting switches, regulators, etc, these 
boards shall be well varnished with pure shellac on all 
four sides (both inside and out side), irrespective of 
being painted to match the surroundings. The size of 
such boards shall depend on the number of accessories 
that could conveniently and neatly be arranged. Where 
there is danger of attack by white ants, the boards shall 
be treated with suitable anti-termite compound and 
painted on both sides. 



Similar part of all switches, lampholders, distribution 
fuse-boards, ceiling roses, brackets, pendants, fans and 
all other fittings shall be so chosen that they are of the 
same type and interchangeable in each installation. 
Electrical equipment which form integral part of wiring 
intended for switching or control or protection of 
wiring installations shall conform to the relevant Indian 
Standards wherever they exist. 

7.1 Ceiling Roses 

7.1.1 Ceiling rose shall not be used on a circuit the 
voltage of which normally exceeds 250 V. Ceiling 
roses may be of the 2-plate pattern and must have an 
earth terminal. The 3-plate type is used to enable the 
feed to be looped at the ceiling rose rather than to use 
an extra cable which would be needed to loop it at the 
switch. Figure 57 gives different types of ceiling roses. 

7.1.2 For PVC sheathed wiring it is possible to 
eliminate the need for joint boxes if 3-plate ceiling roses 
are employed. No ceiling rose may be used on a circuit 
having a voltage normally exceeding 250 V. Not more 
than two flexible cords may be connected to any one 
ceiling rose unless the later is specially designed for 
multiple pendants. 

7.1.3 Special 3 and 4-pin fittings rated at 2 or 6 A 
may be obtained and these can be installed where 
lighting fittings need to be removed or rearranged. 
The ability to remove lighting easily can assist in 



92 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 






57A Porcelain Ceiling Rose 
with Two Plates 



57B Porcelain Ceiling Rose 
with Three Plates 



57C Ceiling Rose Made of 
Bakelite or Plastic 



Fig. 57 Ceiling Rose 



carrying our maintenance. Although the fitting is a 
socket outlet, it cannot be used for supplying hand 
held equipment. 

7.1.4 For the conduit system of wiring it is usual to fit 
ceiling roses which screw direct on to a standard 
conduit box, the box being fitted with an earth 
terminal. 

7.2 Luminaries 

7.2.1 Every luminaire or group of luminaries must be 
controlled by a switch or a socket outlet and plug, 
placed in a readily accessible position. Luminaire 
should conform to relevant Indian Standard where 
existing. 

7.2.2 In damp situations, every luminaire shall be of 
the water proof type, and in situations where there is 
likelihood of presence of flammable or explosive dust, 
vapour, or gas, the luminaries must be of the flameproof 
type in accordance with the recommendation of Part 7 
of this Code and relevant Indian Standard (see IS 5571). 
Flammable shade shall not form a part of lighting 
fittings unless such shade is well protected against all 
risks of fire. Celluloid shade or lighting fittings shall 
not be used under any circumstances. General and 
safety requirements for electrical lighting fittings shall 
be in accordance with good practice. The lighting 
fittings shall conform to relevant Indian Standards 
where they exist. 

The use of fittings- wire shall be restricted to the internal 
wiring of the lighting fittings. Where fittings wire is 
used for wiring fittings, the sub-circuit loads shall 
terminate in a ceiling rose or box with connectors from 
which they shall be carried into the fittings 

7.2.3 Flexible Cords and Cables 

7.2.3 .1 The conductor of flexible cords and cables shall 
be according to flexibility Class 5 of IS 8130. Flexible 



cords, if not properly installed and maintained, can 
become a cause of fire and shock. Flexible cords must 
not be used for fixed wiring. Flexible cords must not 
be used where exposed to dampness or immediately 
below water pipes. They should be open to view 
through out their entire length, except where passing 
through a ceiling when they must be protected with a 
properly bushed non-flammable tube. Flexible cords 
must never be held in position by means of insulated 
staples. Connections between flexible cords and cables 
shall be effected with an insulated connector, and this 
connector must be enclosed in a box or in part of a 
luminaire. If an extension of a flexible cord is made 
with a flexible cord connector consisting of pins and 
sockets, the sockets must be fed from the supply, so 
that the exposed pins are not alive when disconnected 
from the sockets. All flexible cords used for portable 
appliances shall be of the sheathed circular type and, 
therefore twisted cords must not be used for portable 
handlamps, floor and table lamps, etc. All flexible cords 
should be frequently inspected, especially at the point 
where they enter lampholders and other accessories, 
and renewed if found to be unsatisfactory. Flexible 
cords used in workshops and other places subjected to 
risk of mechanical damage shall be sheathed or 
armoured. 

7.2.3.2 Where flexible cords support luminaries the 
maximum weight which may be supported is as 
follows: 



Nominal Cross-sectional 


Maximum 


Area of Flexible Cord 


Permissible Weight 


mm 2 


kg 


(1) 


(2) 


0.5 


2 


0.75 


3 


1.0 


5 



PART 1 GENERAL AND COMMON ASPECTS 



93 



SP 30: 2011 



If necessary two or more flexible cords shall be used 
so that the weight supported by any cord does not 
exceed the above values. 

7.2.3.3 In kitchens and sculleries, and in rooms with a 
fixed bath, flexible cords shall be of the PVC sheathed 
or an equally waterproof type. 

7.2.3.4 In industrial premises luminaries shall be 
supported by suitable pipe/conduits, brackets fabricated 
from structural steel, steel chains or similar materials 
depending upon the type and weight of the fittings. 
Where a lighting fitting is supported by one or more 
flexible cords, the maximum weight to which the twin 
flexible cords may be subjected shall be as follows: 



Nominal Cross -sectional 


Maximum Permissible 


Area of Twin Cord 


Weight 


mm 2 


kg 


(1) 


(2) 


0.5 


2 


0.75 


3 


1.0 


5 


1.5 


5.3 


2.5 


8.8 


4.0 


1.4.0 



7.2.3.5 Where the temperature of the luminaire is likely 
to exceed 60° C, special heat-resisting flexible cords 
should be used, including for pendant or enclosed type 
luminaries. The flexible cord should be insulated with 
heatproof insulation such as butyl or silicone rubber. 
Ordinary PVC insulated cords are not likely to 
withstand the heat given off by tungsten filament lamps. 
Flexible cords feeding electric heaters must also have 
heatproof insulation such as butyl or silicone rubber. 

7.3 Lamp Holders 

7.3.1 Insulated lampholders should be used wherever 
possible. Lampholders fitted with switches must be 
controlled by a fixed switch or socket outlet in the same 



room. Lamp holder should conform to relevant Indian 
Standards. 

7.3.2 Lamp holders for use on brackets and the like 
shall be in accordance with Indian Standards and all 
those for use with flexible pendants shall be provided 
with cord grip. All lampholders shall be provided with 
shade carriers. The outer screwed contact of Edison 
screw-type lampholders must always be connected to 
the neutral of the supply. Small Edison screw 
lampholders must have a protective device not 
exceeding 6 A, but the larger sizes may have a protective 
device not exceeding 1 6 A. The small Bayonet Cap (BC) 
lampholder must have a protective device not exceeding 
6 A, and for the larger BC lampholders the protective 
device must not exceed 16 A. Figure 58 shows different 
types of BC lamp holders. 

7.3.3 No lampholder may be used on circuits exceeding 
250 V and all metal lampholders must have an earth 
terminal. In bathrooms and other positions where there 
are stone floors or exposed extraneous conductive parts, 
lampholders should be fitted with insulated skirts to 
prevent inadvertent contact with live pins when a lamp 
is being removed or replaced. 

7.4 Lamps 

7.4.1 All lamps unless otherwise required and suitably 
protected, shall be hung at a height of not less than 

2.5 m above the floor level. All electric lamps and 
accessories shall conform to relevant Indian Standards. 
Portable lamps shall be wired with flexible cord. Hand 
lamps shall be equipped with a handle of moulded 
composition or other material approved for the purpose. 
Hand lamps shall be equipped with a substantial guard 
attached to the lamp holder or handle. Metallic guards 
shall be earthed suitably. 

7.4.2 A bushing or the equivalent shall be provided 
where flexible cord enters the base or stem of portable 
lamp. The bushing shall be of insulating material unless 
a jacketed type of cord is used. All wiring shall be free 







58A Pendant Holder 



58B Bracket Holder 58C Batten Holder 

Fig. 58 Different Types of Bayonet Holders 



58D Push-pull Holder 



94 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



from short-circuits and shall be tested for these defects 
prior to being connected to the circuit. Exposed live 
parts within porcelain fixtures shall be suitably recessed 
and so located as to make it improbable that wires will 
come in contact with them. There shall be a spacing of 
atleast 125 mm between live parts and the mounting 
plane of the fixture. 

7.4.3 External and road lamps shall have weatherproof 
fittings of approved design so as to effectively prevent 
the ingress of moisture and dust. Flexible cord and cord 
grip lamp holders shall not be used where exposed to 
weather. In verandahs and similar exposed situations 
where pendants are used, these shall be of fixed rod 
type. 

7.5 Socket Outlets and Plugs 

7.5.1 Socket outlets are used for circuits not exceeding 
250 V. Figure 59 shows various accessories and their 
use. Each 16A socket-outlet provided in buildings for 
the use of domestic appliances shall be provided with 
its own individual fuse or miniature circuit-breaker 
(MCB), with suitable discrimination with back-up fuse 
or miniature circuit-breaker provided in the 
distribution/sub-distribution board. The socket-outlet 
shall not necessarily embody the fuse or MCB as an 
integral part of it. Each socket-outlet shall also be 
controlled by a switch which shall preferably be located 
immediately adjacent thereto or combined therewith. 
The switch controlling the socket-outlet shall be on 



the live side of the line. Ordinary socket-outlet may be 
fixed at any convenient place at a height above 20 cm 
from the floor level and shall be away from danger of 
mechanical injury. Socket outlets installed in old 
people's homes and in domestic premises likely to be 
occupied by old or disabled people, should be installed 
at not less than 1 m from floor level. 

In situations where a socket-outlet is accessible to 
children, it is necessary to install an interlocked plug 
and socket or alternatively a socket-outlet which 
automatically gets screened by the withdrawal of plug. 
In industrial premises socket-outlet of rating 16 A and 
above shall preferably be provided with interlocked 
type switch. Socket outlets should conform to relevant 
Indian Standards. 

7.5.2 In an earthed system of supply, a socket-outlet 
with plug shall be of three-pin type with the third 
terminal connected to the earth. When such socket- 
outlets with plugs are connected to any current 
consuming device of metal or any non-insulating 
material or both, conductors connecting such current- 
consuming devices shall be of flexible cord with an 
earthing core and the earthing core shall be secured by 
connecting between the earth terminal of plug and the 
body of current-consuming devices. 

In industrial premises three phase and neutral socket- 
outlets shall be provided with a earth terminal either 
of pin type or scrapping type in addition to the main 




FIXED SOCKET OUTLET 

PLUG (NON-REWIRABLE) 

CORD EXTENSION SET 



|j£»— *» 



i 

PLUG AND SOCKET-OUTLET 



PORTABLE SOCKET-OUTLET 
(NON'REWIREABLE) 



PLUG (NON-REWiREABLE>; 




CONNfCTOR 
(NON-REWIR6ABLE) 



APPLIANCE COUPLER 



Fig. 59 Plug Socket Outlet and Associated Accessories 



PART 1 GENERAL AND COMMON ASPECTS 



95 



SF 30 : 2011 



pins required for the purpose. In wiring installations, 
metal clad switch, socket-outlet and plugs shall be used 
for power wiring. 

A recommended schedule of socket-outlets in a residential 
building is given at Table 2 of Part 3 of this Code. 

Although 16 A socket-outlet is extensively used in 
industrial premises, other industrial type socket-outlets 
include single-phase and three-phase sockets with 
ratings up to 125 A. 

The low voltage electrical equipment (safety) standards 
require equipment to be safe. Any part intended to be 
electrified should be adequately protested such that it 
is not accessible to a finger, including that of a child. 
This protection can be achieved by partly shrouding 
the live pins of plugs so that when the plug is in the 
process of being inserted even the smallest finger 
cannot make contact with live metal. 

When installing socket outlets the cables must be 
connected to the correct terminals, which are; 

a) red wire (phase or outer conductor) to 
terminal marked L. 

b) black wire (neutral or middle conductor) to 
terminal marked N. 

c) yellow/ green earth wire to terminal marked 
E. 

7.5.3 If wrong connections are made to socket outlets 
it may be possible for a person to receive an electric 
shock from an appliance when it is switched off. 
Socket-outlet adaptors which enable two or more 
appliances to be connected to a single socket should 
contain fuses to prevent the socket-outlet from 
becoming overloaded, 

7.6 Switches 

7.6.1 There are various types of switches available, the 
most common being the 6 A switch which is used to 
control lights. There is also the 16 A switch for circuits 
carrying heavier currents. For ac circuits the micro- 
gap switch is also being used; it is much smaller than 
the older type and more satisfactory for breaking 
inductive loads. 

Quick-make and slow-break switches are 
recommended for ac. A quick-break switch connected 
to an ac supply and loaded near to its capacity will 
tend to break down to earth when used to switch off an 
inductive load (such as fluorescent lamps). 

7.6.2 In a room containing a fixed bath, switches must 
be fixed out of reach of the person in the bath, 
preferably out side the door, or be of the ceiling type 
operated by a cord. All single pole switches shall be 
fitted in the same conductor though out the installation, 
which shall be the phase conductor of the supply. 



7.6.3 In damp situations, every switch shall be of the 
waterproof type with suitable screwed entries or glands 
to prevent moister entering the switch. To prevent 
condensed moisture from collecting inside a watertight 
switchbox, a very small hole should be drilled in the 
lowest part of the box to enable the moisture to drain 
away. 

7.6.4 Flame proof switches must be fitted in all 
positions exposed to flammable or explosive dust, 
vapour, gas. 

7.7 Fans 

7.7.1 Ceiling Fans 

Ceiling fans including their suspension shall conform 
to Indian Standards. The following should be adhered 
to during installation: 

a) Control of a ceiling fan shall be through its 
own regulator as well as a switch in series. 

b) All ceiling fans shall be wired with normal 
wiring to ceiling roses or to special connector 
boxes to which fan rod wires shall be 
connected and suspended from hooks or 
shackles with insulators between hooks and 
suspension rods. There shall be no joint in the 
suspension rod, but if joints are unavoidable 
then such joints shall be screwed to special 
couplers of 50 mm minimum length and both 
ends of the pipes shall touch together within 
the couplers, and shall in addition be secured 
by means of split pins; alternatively, the two 
pipes may be welded. The suspension rod shall 
be of adequate strength to withstand the dead 
and impact forces imposed on it. Suspension 
rods should preferably be procured along with 
the fan. 

c) Fan clamps shall be of suitable design 
according to the nature of construction of 
ceiling on which these clamps are to be fitted. 
In all cases fan clamps shall be fabricated from 
new metal of suitable sizes and they shall be 
as close fitting as possible. Fan clamps for 
reinforced concrete roofs shall be buried with 
the casting and due care shall be taken that 
they shall serve the purpose. Fan clamps for 
wooden beams, shall be of suitable flat iron 
fixed on two sides of the beam and according 
to the size and section of the beam one or two 
mild steel bolts passing through the beam shall 
hold both flat irons together. Fan clamps for 
steel joist shall be fabricated from flat iron to 
fit rigidly to the bottom flange of the beam. 
Care shall be taken during fabrication that the 
metal does not crack while hammer to shape. 



96 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



Other fan clamps shall be made to suit the 
position, but in all cases care shall be taken to 
see that they are rigid and safe. 

d) Canopies on top and bottom of suspension 
rods shall effectively conceal suspensions and 
connections to fan motors, respectively. 

e) The lead-in-wire shall be of nominal cross- 
sectional area not less than 1 .0 mm 2 copper or 
1.5 mm 2 aluminium and shall be protected 
from abrasion. 

f) Unless otherwise specified, the clearance 
between the bottom most point of the ceiling 
fan and the floor shall be not less than 2.4 m. 
The minimum clearance between the ceiling 
and the plane of the blades shall be not less 
than 300 mm. 

NOTE — All fan clamps shall be so fabricated that fans 
revolve steadily. 

7.7.2 Exhaust Fans 

For fixing of an exhaust fan, a circular hole shall be 
provided in the wall to suit the size of the frame which 
shall be fixed by means of rag-bolts embedded in the 
wall. The hole shall be neatly plastered with cement 
and brought to the original finish of the wall. The 
exhaust fan shall be connected to exhaust fan point 
which shall be wired as near to the hole as possible by 
means of a flexible cord, care being taken that the 
blades rotate in the proper direction. 

7.7.3 Fannage 

7.7.3.1 Where ceiling fans are provided, the bay sizes 



of a building, which control fan point locations, play 
an important part. Fans normally cover an area of 9 m 2 
to 10 m 2 and therefore in general purpose office 
buildings, for every part of a bay to be served by the 
ceiling fans, it is necessary that the bays shall be so 
designed that full number of fans could be suitably 
located for the bay, otherwise it will result in ill- 
ventilated pockets. In general, fans in long halls may 
be spaced at 3 m in both the directions. If building 
modules do not lend themselves for proper positioning 
of the required number of ceiling fans, such as air 
circulators or bracket fans would have to be employed 
for the areas uncovered by the ceiling fans. For this, 
suitable electrical outlets shall be provided although 
result will be disproportionate to cost on account of 
fans. 

7.7.3.2 Proper air circulation could be achieved either 
by larger number of smaller fans or smaller number of 
larger fans. The economics of the system as a whole 
should be a guiding factor in choosing the number and 
type of fans and their locations. 

Exhaust fans are necessary for spaces, such as 
community toilets, kitchens, canteens and godowns to 
provide the required number of air changes 
(see Part 1/Sec 1 1 of this Code). Since the exhaust fans 
are located generally on the outer walls of a room 
appropriate openings in such walls shall be provided 
for in the planning site. 

Positioning of fans and light fittings shall be chosen to 
make these effective without causing shadows and 
stroboscopic effect on the working planes. 



ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS RELATED TO INSTALLATION 



IS No. Title IS No. 

371 : 1999 Ceiling roses — Specification 2412 : 1975 

732 : 1989 Code of practice for electrical wiring 2667 : 1988 

installations 
1255 : 1983 Code of practice for installation and 3043 : 1987 

maintenance of power cables upto 3419 : 1938 

and including 33 kV rating 
1293 : 2005 Plugs and socket-outlets of rated 3439 : 1966 

voltages up to and including 250 V 

and rated current up to and including 3gQg . j 979 

16 A — Specification 
1646 : 1997 Code of practice for fire safety of ^%y] • 1975 

buildings (general): Electrical 

installations 



Title 

Link clips for electrical wiring 
Fittings for rigid steel conduits for 
electrical wiring 
Code of practice for earthing 
Fittings for rigid non-metallic 
conduits 

Flexible steel conduits for electrical 
wiring 

Method of test for non- 
combustibility of building materials 
Accessories for rigid steel conduits 
for electrical wiring 



PART 1 GENERAL AND COMMON ASPECTS 



97 



SP 30 : 2011 



ISNa 
3854 : 1997 

3961 

(Part 1) : 1967 
(Part 2) : 1967 

(Part 3) : 1968 
(Part 5) : 1968 
4289 

(Part 1) : 1984 
(Part 2) : 2000 
4649 : 1968 

5571 : 2000 

5572 : 1994 



6946 : 1990 

8130: 1984 

8623 

(Part 1) : 1993/ 
IEC 60439-1 : 
1985 

(Part 2): 1993/ 
IEC 60439-2 : 
1987 

(Part 3) : 1993/ 
IEC 60439-3 : 
1990 
9537 

(Part 2): 1981 
(Part 3): 1983 

(Part 4); 1983 

(Part 5) : 2000 



Title 

Switches for domestic and similar 

purposes 

Recommended current ratings for 

cables: 

Paper insulated lead sheathed cables 

PVC insulated and PVC sheathed 

heavy duty cables 

Rubber insulated cables 

PVC insulated light duty cables 

Specification for flexible cables for 

lifts and other flexible connections: 

Elastomer insulated cables 

PVC insulated circular cables 

Adaptors for flexible steel conduits 

Guide for selection of electrical 

equipment for hazardous areas 

Classification of hazardous areas 

(other than mines) having flammable 

gases and vapours for electrical 

installation 

PVC insulated cables for working 

voltages upto and including 1 100 V 

Conductors for insulated electric 

cables and flexible cords 

Specification for low-voltage 

switchgear and controlgear assemblies: 

Requirements for type-tested and 

partially type-tested assemblies 

Particular requirements for busbar 
trunking systems (busway) 

Particular requirements for 

equipment where unskilled persons 

have access for their use 

Conduits for electrical installations: 

Rigid steel conduits 

Rigid plain conduits of insulating 

materials 

Pliable self-recovering conduits of 

insulating materials 

Pliable conduits of insulating 

material 



IS No. Title 

(Part 6) : 2000 Pliable conduits of metal or 

composite materials 
(Part 8) : 2003 Rigid non-threadable conduits of 

aluminium alloy 

Fire hazard testing: Part 2 Test 

methods, Section 1 Glow-wire test 

and guidance 



11000(Part2/ 
Seel): 1984/ 
IEC 695-2-1 : 
1980 

11353: 1985 



13703 (Part 1) : 
1993 /IEC 269- 
1 : 1986 

14255 : 1995 



14763 : 2000 



14768 (Part 1) : 
2000 

14772 : 2000 



14927 

(Part 1) : 2001 
(Part 2): 2001 



14930 

(Part 1) : 2001 
(Part 2): 2001 

SP 69 : 2000 



Guide for uniform system of marking 

and identification of conductors and 

apparatus terminals 

LV Fuses for voltages not exceeding 

1000 V ac or 1500 V dc: Part 1 

General requirements 

Aerial bunched cables for working 

voltages upto and including 1 100 V 

— Specification 

Conduits for electrical purposes — 
Outside diameters of conduits for 
electrical installation and threads for 
conduits and fittings — Specification 
Conduit fittings for electrical 
installations — Specification: Part 1 
General requirements 
General requirements for enclosures 
of accessories for household and 
similar fixed electrical installations 

— Specifications for an accessory or 
luminaries 

Cable trunking and ducting systems 

for electrical installations: 

General requirements 

Cable trunking and ducting systems 

intended for mounting on walls or 

ceilings 

Conduit systems for electrical 

installations: 

General requirements 

Particular requirements — Conduit 

systems buried underground 

Banking and related financial 

services — Information security 

guidelines 



98 



NATIONAL ELECTRICAL CODE 



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ANNEX B 
(Clause 6.7.1.0) 

CLASSIFICATION CODING FOR CONDUIT SYSTEMS 



The classification coding format for declared properties 
of the conduit system which may either be incorporated 
in the manufacturer's literature or marked on the 
product shall be as shown below. When the conduit is 
marked with the classification code, it includes at least 
the first four digits. 

a) First digit — Resistance to compression 

[See 6.1.1 of IS 14930 (Part 1)] 



Very light compression strength 
Light compression strength 
Medium compression strength 
Heavy compression strength 
Very heavy compression strength 

b) Second digit — Resistance to impact 

[See 6.1.2 of IS 14930 (Part 1)] 

Very light impact strength 
Light impact strength 
Medium impact strength 
Heavy impact strength 
Very heavy impact strength 

c) Third digit — Lower temperature range 

[See Table 1 of IS 14930 (Part 1)] 

+ 5°C 
-5°C 
-15°C 
-25°C 
-45°C 

d) Fourth digit — Upper temperature range 

[See Table 2 of IS 14930 (Part 1)] 

+ 60°C 
+ 90°C 
+ 105°C 
+ 120°C 
+ 150°C 
+ 250°C 
+ 400°C 

e) Fifth digit — Resistance to bending 

[See 6.1.3 of IS 14930 (Part 1)] 

Rigid 

Pliable 

Pliable/Self recovering 

Flexible 



1 

2 
3 
4 
5 



1 
2 
3 
4 

5 



1 

2 
3 
4 



f) Sixth digit — Electrical characteristics 

[See 6.3 of IS 14930 (Part 1)] 

None declared 

With electrical continuity characteristics 
With electrical insulating characteristic 
With electrical continuity and insulating 
characteristics 



g) Seventh digit — Resistance to ingress of solid 
objects 



[See 6.4.1 of IS 14930 (Part 1)] 

Protected against solid foreign objects 

2.5 mm diameter and greater 
Protected against solid foreign objects 

1.0 diameter and greater 
Dust protected 
Dust tight 

h) Eight digit — Resistance to ingress of water 

[See 6.4.2 of IS 14930 (Part 1)] 

None declared 

Protected against vertically falling water drops 
Protected against vertically falling water drops 
when conduit system tilted up to an angle of 15° 
Protected against spraying/ water 
Protected against splashing water 
Protected against water jets 
Protected against powerful water jets 
protected against the effects of temporary 
immersion in water 

j) Ninth digit — Resistance against corrosion 

[See 6 A3 of IS 14930 (Part 1)] 

Low protection inside and outside 1 

Medium protection inside and outside 2 

Medium protection inside, high protection outside 3 
High protection inside and outside 4 

k) Tenth digit — Tensile strength 
[See, 6.1.4 of IS : 14930 (Part 1)] 



3 

4 

5 
6 





1 

2 

3 
4 
5 
6 

7 



None declared 
Very light tensile strength 
Light tensile strength 
Medium tensile strength 
Heavy tensile strength 
Very heavy tensile strength 



PART 1 GENERAL AND COMMON ASPECTS 



99 



SP 30: 2011 

m) Eleventh digit — Resistance to flame None declared 

propagation Very light suspended load capacity 1 

Light suspended load capacity 2 

[See 6.5 of IS 14930 (Part 1)] j^ ^^ loa / capa y dty 3 

Non-flame propagating 1 Heavy suspended load capacity 4 

Flame propagating 2 Very heavy suspended load capacity 5 

n) Twelfth digit — Suspended load capacity p) Thirteenth digit — Fire effects 

[See 6.1.5 of IS 14930 (Part 1)] (Under consideration) 



100 NATIONAL ELECTRICAL CODE 



SP 30: 2011 



SECTION 10 SHORT-CIRCUIT CALCULATIONS 



FOREWORD 

Circuit calculations are performed for checking the 
adequacy of the electrical equipment for any electrical 
system that is characterized by the type of distribution 
system comprising of transformers, bus, cables etc. 

The essential requirements and methods associated 
with following calculations are covered in this Section: 

a) Short circuit calculations in 3 phase ac systems. 

b) Current carrying capacity and Voltage drop 
calculations for cables and flexible cords. 

Assistance for this Section has been derived from the 
following standards: 

IS No. Title 

13234 : 1992 Guide for short circuit calculation 

in three phase ac systems 

1 3235 : 1 99 1/ Calculation of the effects of short 
IEC 865 (1986) circuit currents 

1 SCOPE 

This Part 1/Section 10 covers guidelines and general 
requirements associated with circuit calculations, 
namely, short circuit calculations and voltage drop 
calculations for cables and flexible cords. 

2 REFERENCES 

The following Indian Standards have been referred in 
this Section: 



IS No. 
2086 : 1993 



9926: 1981 



13703 (Part 2/ 
Sec 1) : 1993/DEC 
60269-2 : 1986 



13703 (Part 2/ 
Sec 2) : 1993/IEC 
60269-2 : 1987 



IS/IEC 60898-1 : 
2002 



Title 

Carriers and bases used in 
rewirable type electric fuses for 
voltages upto 650V 
Fuse wires used in rewirable type 
electric fuses upto 650 V 
Specification for low-voltage 
fuses for voltages not exceeding 
1 000 V ac or 1 500 V dc : Part 2 
Fuses for use by authorized 
persons, Section 1 Supplementary 
requirements 

LV fuses for voltages not 
exceeding 1000 V ac or 1500 V dc: 
Part 2 Fuses for use by authorized 
persons, Section 2 Examples of 
standardized fuses 
Electrical accessories — Circuit 
breakers for over protection for 
household and similar installations: 
Part 1 Circuit breakers for ac 
operation 



3 GENERAL CONSIDERATIONS 

3*0 General 

3.0*1 This subject of circuit calculations covers the 
guidelines relating to the short circuit withstand 
capability of the electrical equipment and to check 
permissible voltage drop in cables and flexible cords 
upto the equipment terminals. 

3.0.2 The objective of the circuit calculation is to ensure 
that the selection of equipment under consideration is 
designed for safe and reliable long period of operation. 

4 CIRCUIT CALCULATIONS 

4.1 Short Circuit Calculations 

4.1.1 Design Considerations 

4.1.1.1 A complete calculation of the short-circuit 
currents should give the currents as a function of time 
at the short circuit location from the initiation of the 
short circuit up to its end, corresponding to the 
instantaneous value of the voltage at the beginning of 
the short-circuit. 

4.1.1.2 In most of the practical cases it is sufficient to 
determine the r.m.s value of symmetrical AC 
component and the peak value / p of the short-circuit 
current following the occurrence of a short circuit. The 
value of i depends on time constant of the decaying 
aperiodic component i DC with frequency depending on 
the X/R ratio of the short-circuit impedance. 

4.1.1.3 For determination of asymmetrical short-circuit 
breaking current, the decaying aperiodic component 
/ DC may be calculated with sufficient accuracy by: 



i DC - V2 I k e 



■iKfiT 



where 



/£ = initial symmetrical short circuit current (A), 

/ = nominal system frequency (Hz), 

t = time duration of fault(s), and 

x = time constant based on system X/R. 

4.1.1.4 The calculation of maximum and minimum 
short circuit current are based on the following 
considerations: 

a) For the duration of the short-circuit there is 
no change in the number of circuits involved, 
that is, a three phase short-circuit remains as 
three phase and similarly a line-to-earth short- 
circuit remains line-to-earth during the short 
circuit. 



PART 1 GENERAL AND COMMON ASPECTS 



101 



SP 30 : 2011 



b) Tap changers of the transformer are at 
nominal position. 

c) Arc resistances are not taken into account. 

4.1.1.5 In situations where there will be no significant 
change in ac component decay due to far distance from 
generator (see Fig. 1), short-circuit current can be 
considered as the sum of the following two 
components: 



a) The ac component with constant amplitude 
during the whole short-circuit. 

b) The aperiodic component beginning with 
initial value A and decaying to zero. 

4.1,1.6 For the systems where there will be significant 
change in ac component decay due to close location 
near Generator (see Fig. 2), short circuit- current can be 
considered as the sum of the following two components: 



Current 



Top envelope 

dec aying (aperiodic) component /qq 




Time 



Bottom envelope 



Fig. 1 Short-Circuit Current at a System Far-from-Generator 



Current 



Top envelope 

decaying (aperiodic) component j'qq 




Time 



/ k = initial symmetrical short-circuit current 

/ p = peak short-circuit current 

/ k = steady-state short-circuit current 

/ DC = decaying (aperiodic) component of short-circuit current 

A = initial value of the aperiodic component / DC 

Fig. 2 Short-Circuit Current at a System Near-to-Generator 



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a) The ac component with decaying amplitude 
during the whole short circuit. 

b) The aperiodic component beginning with 
initial value A and decaying to zero. 

4.1.2 Calculation Methods 

4.1.2.1 General 

Equivalent circuits are to be drawn for the system 
before calculation of short-circuit current with example 
as per Fig. 3. 

4*1.2.1.1 Balanced short-circuit 

The balanced three-phase short-circuit of a three-phase 
ac system often leads to the highest values of 
prospective (available) short-circuit current and the 
calculation becomes particularly simple on account of 
the balanced nature of the short circuit. 

In calculating the short-circuit current, it is sufficient 
to take into account only the positive sequence short- 
circuit impedance, Z (1) = Z^ as seen from the fault 
location. 



4.1.2.1.2 Unbalanced short-circuit 

The following types of unbalanced (asymmetrical) 
short-circuits are to be considered: 



Q 



'KQ 



<3> 



< t :1 



SP 30 : 2011 

a) line-to-line short-circuit without earth 
connection 

b) line-to-line short-circuit with earth connection 

c) line-to-earth short-circuit 

Normally, the three-phase short-circuit current is the 
largest among the above listed type of faults. In the 
event of a short-circuit near to a transformer with 
neutral earthing or a neutral earthing transformer, the 
line-to-earth short-circuit current may be greater than 
the three-phase short-circuit current. This applies in 
particular to transformers of vector group Yz, Dy and 
Dz when earthing the y- or z-winding on the low 
voltage side of the transformer. 

In three-phase systems the calculation of the current 
values resulting from unbalanced short-circuits is 
simplified by the use of the method of symmetrical 
components which requires the calculation of three 
independent system components, avoiding any 
coupling of mutual impedances. 

Using this method, the currents in each line are found 
by superposing the currents of three symmetrical 
component systems: 



a) positive-sequence current 7 ( 



(i)> 



•tih 



NON F 

ROTATING 

LOAD 



jEZI ROTATING 
LOAD 



k3 



3A System Diagram 



R Qt x qt Q Rt 



X't 



R L X l F 



o 



^ 
J3 



3B Equivalent Circuit Diagram (Positive Sequence System) 

Fig. 3 Illustation for Calculating the Initial Symmetrical Short-Circuit Current I" k in Compliance 
with the Procedure for the Equivalent Voltage Source 



PART 1 GENERAL AND COMMON ASPECTS 



183 



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b) negative- sequence current 7 (2) , and 

c) zero-sequence current Z (0) . 

Taking the line LI as reference the currents / L1 / L2 and 
Z L3 are given by: 

(la) 
(lb) 
(lc) 



i-L\~ -(1) + HI) + -(0) 

42 = S 2 Z (J) + aZ (2) + / (0) 
Z L3 = a/ (J) + a Z( 2 ) + Z(0) 



Each of the three symmetrical component systems has 
its own impedance. 

The method of the symmetrical components postulates 
that the system impedances are balanced, for example 
in the case of transposed lines. The results of the short- 
circuit calculation have an acceptable accuracy also in 
the case of un-transposed lines. 

4.1.2.1.3 Short-circuit impedances 

While calculating the impedances, there shall be 
clear distinction between short-circuit impedances 
at the short-circuit location and short-circuit 
impedances of individual electrical equipment. 
Accordingly the calculations with symmetrical 
components namely, positive-sequence, negative- 
sequence and zero-sequence short-circuit 
impedances to be performed. 

4.1.3 Effects Due to Short Circuit 

4.1.3.1 The electromagnetic effect on rigid and slack 
(line) conductors 

With the calculation methods, forces on insulators, 
stresses in rigid conductors and tensile forces in slack 
conductors are to be estimated. 

4.1.3.1.1 Mechanical forces due to short-circuit 
currents 

Currents in parallel conductors will induce 
electromagnetic forces between the conductors. When 
the parallel conductors are long compared to the 
distance between them, the forces will act evenly 
distributed along the conductors. 

When the currents are in opposite directions the 
electromagnetic force is a repulsion which tends to 
induce deformations that would increase inductance 
of the circuit. 

The value of the force in a given direction can be 
calculated by considering the work done in the case of 
a virtual displacement in the actual direction. As the 
work is done by the electromagnetic force, it must be 
equal to the change in the energy in the magnetic field 
caused by this virtual displacement. 

The force between two conductors is proportional to 
the square of the current, or to the product of the two 



currents. As the current is a function of time, the force 
will also be a function of time. In the case of a short- 
circuit current without a dc component the force will 
vary with twice the frequency of the current. A dc 
component in the short-circuit current will give rise to 
an increase of the peak value of the force and to a 
component of force varying with the same frequency 
as the current. The peak value of the force is of 
particular interest in the case of mechanically rigid 
structures. 

The force will result in bending stress on rigid 
conductors, tension stress and deflection in flexible 
conductors and bending, compression or tension loads 
on the supports. 

4.1.3.1.2 Stresses in rigid conductors and forces on 
supports 

The conductors may be supported in different manners, 
either fixed or simple or in a combination of both, and 
may have two, three, four or several supports. 
Depending on the kind of support and the number of 
supports, the stress in the conductors and the forces on 
the supports will be different for the same short-circuit 
current. 

The stresses in the conductors and the forces on 
supports also depend on the ratio between the natural 
frequency of the mechanical system and the frequency 
of the electromagnetic force. Especially in the case of 
resonance, or near to resonance, the stresses and forces 
in the system may be amplified. 

4.1.3.1.3 Tensile forces in slack conductors (line 
conductors) 

A short-circuit current in a slack conductor will cause 
a tensile force in the conductor which will affect 
insulators, support structures and apparatus. It is 
necessary to distinguish between the tensile force 
during short-circuit and the tensile force after short- 
circuit, when the conductor falls back to its initial 
position. 

4.1.3.2 Thermal effect on bare conductors 

The heating of conductors due to short-circuit currents 
involves several phenomena of a non-linear character 
and other factors that have to be either neglected or 
approximated in order to make a mathematical 
approach possible. 

For the purpose of this calculation, the following 
assumptions can been made: 

a) Proximity-effect (magnetic influence of nearby 
parallel conductors) has been disregarded. 

b) Resistance-temperature characteristic has 
been assumed linear. 



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c) The specific heat of the conductor is 
considered constant. 

d) The heating is generally considered adiabatic. 

4.1.3.2.1 Calculation of temperature rise 

The loss of heat from a conductor during the short- 
circuit is very low, and the heating can generally be 
considered adiabatic. Hence the calculation for this can 
also be based on adiabatic conditions. 

When repeated short-circuits occur with a short-time 
interval between them (that is rapid auto-reclosure) the 
cooling down in the short dead-time is of relatively 
low importance, and the heating can still be considered 
adiabatic. In cases where the dead-time interval is of 
longer duration (that is delayed auto-reclosure) the heat 
loss may be taken into account. 

The calculation need not take into account the skin 
effect, that is the current is regarded as evenly 
distributed over the conductor cross-section area. This 
approximation is not valid for large cross-sections, and 
therefore for cross-sections above 600 mm 2 the skin 
effect shall be taken into account. 

NOTE — If the main conductor is composed of sub-conductors, 
uneven current distribution between the sub-conductors will 
influence the temperature rise of sub-conductors. 

4.1.3.2.2 Calculation of thermal equivalent short- 
circuit current 

The thermal equivalent short-circuit current is to be 
calculated using the short-circuit current r.m.s. value 
and the factors m and n for the time-dependent heat 
effects of the dc and ac components of the short-circuit 
current 

The thermal equivalent short-circuit current can be 
expressed by: 



and 



Ah ~ ^ k V m + n 

where m and n are numerical factors, /' k the r.m.s. value 
of the initial symmetrical short-circuit current; in a 
three-phase system, the balanced three-phase short- 
circuit is decisive. The values m and n are usually 
defined as functions of the duration of the short-circuit 
current. For a distribution network usually n = 1. 

NOTE — The relation /" k // k is dependent on the impedance 
between the short-circuit and the source. 

When a number of short-circuits occur with a short 
time interval in between, the resulting thermal 
equivalent short-circuit current is obtained from: 



r k =5X 

i-l 



4.1.3.2.3 Calculation of temperature rise and rated 
short-time current density for conductors 

The temperature rise in a conductor caused by a short- 
circuit is a function of the duration of the short-circuit 
current, the thermal equivalent short-circuit current and 
the conductor material. 

NOTE — The maximum permitted temperature of the support 
has to be taken into account. 

4.1.3.2.4 Calculation of the thermal short-circuit 
strength for different durations of the short-circuit 
current 

Electrical equipment has sufficient thermal short-circuit 
strength as long as the following relations hold for the 
thermal equivalent short-circuit current 7 th : 

/ th </ thr forr v <r kr 



^ for T k >T k 



where I thv is the rated short-time current and T^ the 
rated short- time. 

The thermal short-circuit strength for a bare conductor 
is sufficient when the thermal equivalent short-circuit 
current density S th satisfies the following relation: 



S t u < S* 




1 n 
y k I = i 



thi ^ki 



With Tfo =1 s and for all T k the rated short time current 
density S tht is shown in Fig 4. 

4.2 Calculations for Current Carrying Capacity and 
Voltage Drop for Cables and Flexible Cords 

4.2.1 Conductor Operating Temperature 

The current to be carried by any conductor for sustained 
periods during normal operation shall be such that the 
conductor operating temperature given in the 
appropriate table of current-carrying capacity in this 
section is not exceeded. 

Where a conductor operates at a temperature 
exceeding 70 °C it shall be ascertained that the 
equipment connected to the conductor is suitable for 
the conductor operating temperature. 

4.2.2 Cables Connected in Parallel 

Except for a ring final circuit, cables connected in 



PART 1 GENERAL AND COMMON ASPECTS 



105 




6u 




a) Full lines: Copper 

Dotted lines: Flat product of unalloyed steel and steel cables. 

b) Aluminium, aluminium alloy, aluminium conductor steel reinforced (ACSR). 

Fig. 4 Relation Between Rated Short-time Current Density (T kr =1 s) and Conductor Temperature 
106 NATIONAL ELECTRICAL CODE 



SP 30: 2011 



parallel shall be of the same construction, cross- 
sectional area, length and disposition, without branch 
circuits and arranged so as to carry substantially equal 
currents. 

4.2.3 Cables Connected to Bare Conductors or Bus 
Bars 

Where a cable is to be connected to a bare conductor 
or busbar its type of insulation and/or sheath shall be 
suitable for the maximum operating temperature of the 
bare conductor or busbar. 

4.2.4 Cables in Thermal Insulation 

Where a cable is to be run in a space to which thermal 
insulation is likely to be applied, the cable shall 
wherever practicable be fixed in a position such that it 
will not be covered by the thermal insulation. Where 
fixing in such a position is impracticable the cross- 
sectional area of the cable shall be appropriately 
increased. 

For a single cable likely to be totally surrounded by 
thermally insulating material over a length of more 
than 0.5 m, the current-carrying capacity shall be taken, 
in the absence of more precise information, as 0.5 times 
the current-carrying capacity for that cable clipped 
direct to a surface and open. 

Where a cable is to be totally surrounded by thermal 
insulation for less than 0.5 m the current-carrying 
capacity of the cable shall be reduced appropriately 
depending on the size of cable, length insulation and 
thermal properties of the insulation. The de-rating 
factors have to be appropriate to conductor sizes. 

4.2.5 Metallic Sheaths and/or Non-Magnetic Armour 
of Single-Core Cables 

The metallic sheaths and/or non-magnetic armour of 
single-core cables in the same circuit shall normally 
bonded together at both ends of their run (solid 
bonding). Alternatively the sheaths or armour of such 
cables having conductors of cross-sectional area 
exceeding 50 mm 2 and a non-conducting outer sheath 
may be bonded together at one point in their run (single 
point bonding) with suitable insulation at the un- 
bonded ends, in which case the length of the cables 
from the bonding point shall be limited so that, at full 
load, voltages from sheaths and/or armour to Earth, 

a) do not exceed 25 V 

b) do not cause corrosion when the cables are 
carrying their full load current, and 

c) do not cause danger or damage to property 
when the cables are carrying short-circuit 
current. 



4.2.6 Correction Factors for Current-Carrying 
Capacity 

The current-carrying capacity of cable for continuous 
service is affected by ambient temperature and by 
frequency. This Clause provides correction factors in 
these respects as follows. 

4.2.6.1 Ambient temperature 

In practice the ambient air temperatures may be 
determined by thermometers placed in free air as close 
as practicable to the position at which the cables are 
installed or are to be installed, subject to the proviso 
that the measurements are not to be influenced by the 
heat arising from the cables; thus if the measurements 
are made while the cables are loaded, the thermometers 
should be placed about 0.5 m or ten times the overall 
diameter of the cable whichever is the lesser, from the 
cables, in the horizontal plane, or 150 mm below the 
lowest of the cables. 

Where cables are subject to such radiation due to solar 
or other infra-red, the current-carrying capacity may 
need to be specially calculated. 

4.2.6.2 Grouping 

Appropriate correction factors to be applied to the 
manufacture declared current-carrying capacity where 
cables or circuits are grouped. 

4.2.7 Effective Current-Carrying Capacity 

The current-carrying capacity of cable corresponds to 
the maximum current that can be carried in specified 
conditions without the conductors exceeding the 
permissible limit of steady state temperature for the 
type of insulation concerned. 

The values of current calculated represent the effective 
current- carrying capacity only where no correction 
factor is applicable. Otherwise the current-carrying 
corresponds to the value multiplied by the appropriate 
factors for ambient temperature, grouping and thermal 
insulation, as applicable. 

Irrespective of the type of over current protective device 
associated with the conductors concerned, the ambient 
temperature correction factors to be used when 
calculating current- carrying capacity (as opposed to 
those used when selecting cable size). 

4.2.8 Overload Protection 

Where overload protection is required, the type of 
protection provided does not affect the current-carrying 
capacity of a cable for continuous service (/ z ) but it 
may affect the choice of conductor size. The operating 
conditions of a cable are influenced not only by the 
limiting conductor temperature for continuous service, 
but also by the conductor temperature which might be 



PART 1 GENERAL AND COMMON ASPECTS 



107 



SP 30 : 2011 



attained during the conventional operating time of the 
overload protection device, in the event of an overload. 

This means that the operating current of the protective 
device must not exceed 1.45/ 2 . Where the protective 
device is a fuse as per IS 13703 (Part 2/Section 1) 
and IS 13703 (Part 2/Section 2) or IS 2086 or a 
miniature circuit breaker as per IS/IEC 60898, this 
requirement is satisfied by selecting a value of / z not 
less than I n 

In practice, because of the standard steps in nominal 
rating of fuse and circuit breakers, it is often necessary 
to select a value of I n exceeding I b . In that case, because 
it is also necessary for I z in turn to be not less than the 
selected value of In, the choice of conductor cross- 
sectional area maybe dictated by the over load 
conditions and the current-carrying capacity (I z ) of the 
conductors will not always by fully used. 

The size needed for a conductor protected against 
overload by a IS 9926 fuse fix in rewirable type fuse 
can be obtained by the use of a correction factor, 
1.45/2 = 0.725 which results in the same degree of 
protection as that afforded by other overload protective 
devices. This factor is to be applied to the nominal 
rating of the fuse as a divisor, thus indicating the 
minimum value of 7 t required of the conductor to be 
protected. In this case also, the choice of conductor 
size is dictated by the overload conditions and the 
current carrying capacity (7 Z ) of the conductors can not 
be fully used. 

4.2.9 Determination of the Size of Cable to be Used 

Having established the design current (7 b ) of the circuit 
under consideration, the conductor size has to be sized 
necessarily from consideration of the conditions of 
normal load and overload is then determined. All 
correction factors affecting 7 Z (that is, the factor for 
ambient temperature, grouping and thermal insulation) 
can, if desired, be applied to the values of 7 t as 
multipliers. This involves a process of trial and error 
until a cross-sectional area is reached which ensures 
that 7 Z is not less than 7 b and not less than 7 n of any 
protective device it is intended to select. In any event, 
if a correction factor for protection by a semi-enclosed 
fuse is necessary, this has to be applied to 7 n as a divisor. 
It is therefore more convenient to apply all the 
correction factors to 7 n as divisors. 

4.2.10 Voltage Drop in Consumers' Installations 

4.2.10.1 Acceptable values of voltage drop 

Under normal service conditions the voltage at the 
terminals of any fixed current-using equipment shall 
be greater than the lower limit corresponding to the 
Indian Standard relevant to the equipment. 



Where the fixed current-using equipment concerned 
is not the subject of Indian Standard the voltage at the 
terminals shall be such as not to impair the safe 
functioning of the equipment. 

The requirements are deemed to be satisfied for a 
supply given if the voltage drop between the origin of 
the installation (usually the supply terminal) and the 
fixed current-using equipment does not exceed 
5 percent of the normal voltage of the supply. 

A greater voltage drop may be accepted for a motor 
during starting periods and for other equipment with 
high in-rush currents provided it is verified that the 
voltage variations are within the limits specified in the 
relevant Indian Standards for the equipment or, in the 
absence of an Indian Standard, in accordance with the 
manufacturer' s recommendations . 

4.2.10.2 Calculation of voltage drop 

For a given run, to calculate the voltage drop (mV/A/m) 
the value for the cable concerned has to be multiplied 
by the length of the run in metres and by the current 
the cable is intended to carry, namely the design current 
of the circuit (7 b ) in amperes. 

For three-phase circuits the calculated mV/A/m values 
relate to the line voltage and balanced conditions have 
to be assumed. 

The direct use of the calculated (m/V/A/m) r or 
(mV/A/m) z values, as appropriate may lead to 
pessimistically high calculated values of voltage drop 
or, in other words, to unnecessarily low values of 
permitted circuit lengths. 

Where the design current of a circuit is significantly 
less than the effective current-carrying capacity of the 
cable chosen, the actual voltage drop would be less 
than the calculated value because the conductor 
temperature (and hence its resistance) will be less than 
that on which the calculated mV/A/m had been based. 

In some cases it may be advantageous to take account 
of the load power factor when calculating voltage drop. 

4.2.10.3 Correction Factor for operating temperature 

For cables having conductors of cross-sectional area 
16 mm 2 or less the design value of mV/A/m is obtained 
by multiplying the calculated value by a factor C t , given by 



/ 



230 + t p - 



C t = 



r 2 ^ 



(* p -30) 



230+ u 



where t = maximum permitted normal operating 
temperature, in ° C. 

NOTE — For convenience, the above formula is based on the 
resistance-temperature coefficient of 0.004 per °C at 20°C for 
both copper and aluminum conductors. 



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For very large conductor sizes where the resistive 
component of voltage drop is much less than the 
corresponding reactive part (that is when xlr > 3) this 
correction factor need not be considered. 

4.2.10.4 Correction for load power factor 

For cables having conductors of cross-sectional area 
of 16 mm 2 or less the design value of mV/A/m is 
obtained approximately by multiplying the calculated 
value by the power factor of the load, cos 9. 

For cables having conductors of cross-sectional area 
greater than 16 mm 2 the design value of m/V/A/m is 
approximately: 

Cos (p [Calculated (m/V/A/m) r ] + sin (p [Calculated 
(m/V/A/m)J 

For single-core cables in flat formation the calculated 



values apply to the outer cables and may under-estimate 
for the voltage drop between an outer cable and the 
centre cable for cross-sectional areas above 240 mm 2 
and power factors greater than 0.8. 

4.2.10.5 Combined correction for both operating 
temperature and load power factor 

Where it is considered appropriate to correct the 
calculated mV/A/m value so for both operating 
temperature and load power factor, the design values 
of mV/A/m are given by: 



a) 



b) 



for cable having conductors of 16 mm 2 or less 
cross-sectional area 
C t cos (p (Calculated mV/A/m) 
for cables having conductors of cross- 
sectional area greater than 16 mm 2 
C t cos cp (Calculated mV/A/m) r ) + sin (p 



PART 1 GENERAL AND COMMON ASPECTS 



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SP- 30: 2011 

SECTION 11 ELECTRICAL ASPECTS OF BUILDING SERVICES 



FOREWORD 

Most of the modern day services in buildings depend 
on electrical energy. These services, broadly; are: 

a) Lighting and ventilation, 

b) Air-conditioning and heating, and 

c) Lifts and escalators. 

From the point of view of conservation of energy and 
safety in its use, it is found essential to draw attention 
to essential design principles for building services. 

Apart from the three major power consuming services 
in a building there are other functional/safety services 
that are basically light current installations, whose 
proper functioning is important. These are: 

a) Electrical audio systems, 

b) Fire-alarm and fighting systems, 

c) Electric call-bell systems, 

c) Electric clock systems, 

d) Computer system, 

e) Telephone systems, and 

f) Building management systems. 

Attention should be paid to the requirements to be 
complied within the design and construction of 
building services. This Section provides basic 
information on the electrical aspects of building 
services. Further details can be had from the relevant 
Indian Standards. 

1 SCOPE 

This Part 1 /Section 1 1 of the Code covers requirements 
for installation work relating to building services that 
use electric power. 

NOTE — SP 7 'National Building Code of India' should be 
referred for non-electrical aspects of building services. 

2 REFERENCES 

A list of Indian Standards related to building services 
is given at Annex A. 

3 GENERAL GUIDELINES 

3.1 Extensive guidelines on building design aspects 
have been covered in SP 7 from the point of view of 
ensuring economic services in an occupancy. These 
shall be referred to from the point of view of ensuring 
good design of building services and early coordination 
amongst all concerned. 



3.2 Orientation of Building 

3.2.1 The chief aim of orientation of buildings is to 
provide physically and psychologically comfortable 
living inside the buildings by creating conditions which 
suitably and successfully ward off the undesirable 
effects of severe weather to a considerable extent by 
judicious use of the recommendations and knowledge 
of climatic factors. 

3.2.2 From the point of view of lighting and ventilation, 
the following climatic factors influence the optimum 
orientation of the buildings: 

a) Solar radiation and temperature, 

b) Clouds, 

c) Relative humidity, and 

d) Prevailing winds. 

IS 7662 (Part 1) gives recommendations on orientation 
of buildings. 

4 ASPECTS OF LIGHTING SERVICES 

4.1 Principles of Good Lighting 

4.1.1 Good lighting is necessary for all buildings and 
has three primary aims. The first is to promote the work 
and other activities carried on within the buildings; the 
second is to promote the safety of people using the 
building; and the third is to create, in conjunction with 
the structure and decoration, a pleasing environment 
conducive to interest and a sense of well-being. 

Realization of these aims involves: 

a) Careful planning of the brightness and colour 
patterns within the working area and the 
surroundings so that attention is drawn 
naturally to the important areas, detail is seen 
quickly and accurately and the room is free 
from any sense of gloom or monotony. 

b) Using directional lighting, where appropriate, 
to assist preception of task detail and to give 
good modelling. 

c) Controlling direct and reflected glare from 
light sources to eliminate visual discomfort, 

d) In artificial lighting installations, minimizing 
flicker from certain types of lamp and paying 
attention to the colour rendering properties 
of the light. 

e) Correlating lighting throughout the building 
to prevent excessive differences between 
adjacent areas and so as to reduce the risk of 
accidents, and 



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f) Installing emergency lighting systems where 
necessary. 

4.1.2 Good lighting design shall take into account the 
following: 

a) Planning the brightness pattern from the point 
of view of visual performance, safety and 
amenity and surroundings; 

b) Form of texture in the task area and 
surroundings; 

c) Controlling glare, stroboscopic effect and flicker; 

d) Colour rendering; 

e) Lighting for movement; 

f) Provision for emergency; 

g) Maintenance factors in lighting installation; 
and 

h) Maximum energy effectiveness of the lighting 
system used consistent with the specific needs 
of visual tasks performed. 

4.1.3 Guidelines on principles of good lighting design 
can be had from IS 3646 (Part 1). Reference should be 
made to National Lighting Code, which covers all 
aspects of lighting. 

4.2 Design Aspect 

4.2.1 Illumination Levels 

The level of illumination for a particular occupation 
depends on the following criteria: 

a) Adequacy for preventing both strain in seeing 
and liability to accidents caused by poor 
visibility, 

b) Adequacy for realizing maximum visual 
capacity, 

c) Adequacy for the performance of visual tasks 
at satisfactory high levels of efficiency, and 

d) Adequacy for pleasantness or amenity. 

4.2.2 Designing for Daylight 

Reference shall be made to IS 2440 and National 
Lighting Code. 

4.2.3 Lighting Problems and Economics 

Reference is drawn to Annexes C and D of IS 3646 
(Part 1) and National Lighting Code. 

5 ASPECTS OF VENTILATION 

5.0 General 

5.0.1 Ventilation of buildings is required to supply fresh 
air for respiration of occupants, to dilute inside air to 
prevent vitiation by body odours and to remove any 
products of combustion or other contaminants in air 
and to provide such thermal environments as will assist 



the maintenance of heat balance of the body in order 
to prevent discomfort and injury to health of the 
occupants. 

5.0.2 The following govern design considerations: 

a) Supply of fresh air for respiration, 

b) Removal of combustion products or other 
contaminants and to prevent vitiation by body 
odours, 

c) Recommended schedule of values of air 
changes for various occupancies, and 

d) The limits of comfort and heat tolerance of 
the occupants. 

5.1 Methods of Ventilation 

General ventilation involves providing a building with 
relatively large quantities of outside air in order to 
improve general environment of building. This may 
be achieved in one of the following ways: 

a) Natural supply and natural exhaust of air, 

b) Natural supply and mechanical exhaust of air, 

c) Mechanical supply and natural exhaust of air, 
and 

d) Mechanical supply and mechanical exhaust 
of air. 

5.2 Mechanical Ventilation 

Reference should be made to IS 3103 and IS 3362 
which cover methods of mechanical ventilation. 

6 ASPECTS OF AIR-CONDITIONING AND 
HEATING SERVICES 

6.1 General 

The object of air-conditioning facilities in buildings 
shall be to provide conditions under which people can 
live in comfort, work safely and efficiently. It shall aim 
at controlling and optimizing factors in the building 
like air purity, air movement, dry bulb temperature, 
relative humidity, noise and vibration, energy efficiency 
and fire safety. 

6.1.1 The design of the system and its associated 
controls should take into account the following: 

a) The nature of the application, 

b) The type of construction of building, 

c) External and internal load patterns, 

d) Desired space conditions, 

e) Permissible control limits, 

f) Control methods for minimizing use of 
primary energy, 

g) Opportunities for heat recovery, 



PART 1 GENERAL AND COMMON ASPECTS 



111 



SP 30 : 2011 



h) Economic factors (including probable future 

cost and availability of power), 

j) Outdoor air quality, 

k) Energy efficiency, 

m) Filteration standard, 

n) Hours of use, 

p) Outdoor air quality, and 

q) Diversity factor. 

6.1.2 The operation of the system in the following 
circumstances should be considered when assessing 
the complete design: 

a) In summer; 

b) In monsoon; 

c) In winter; 

d) In intermediate seasons; 

e) At night; 

f) At weekends and holidays; 

g) Under frost conditions, where applicable; 

h) If electricity supply failure occurs and when 
the supply is restored; and 

j) If extended low voltage conditions persist. 

6.1.3 Consideration should be given to changes in 
building load and the system design so that maximum 
operational efficiency is maintained under part load 
conditions. Similarly, the total system should be 
separated into smaller increments having similar load 
requirements so that each area can be separately 
controlled to maintain optimum operating conditions. 

6.2 Electrical Requirements 

6.2.1 Conduits 

Where conduits are used for carrying insulated 
electrical conductors and when such conduits pass from 
a non-air-conditioned area into an air-conditioned area 
or into a fan chamber of duct, a junction box shall be 
installed or other means shall be adopted to break the 
continuity of such conduit at the point of entry or just 
outside, and the conduit should be sealed round the 
conductors to prevent air being carried from one area 
into the other through the conduit and thereby giving 
rise not only to leakage and inefficiency but also to the 
risk of condensation of moisture inside the conduits. 
The same method applies equally to other types of 
wiring, like wood sheathing or ducts which allow air 
to pass through around the conductors. 

6.2.2 In case of air-conditioning plants where re- 
heating is used, a safety device shall be incorporated 
in the installation to cut off automatically the source 



of heating, such as steam or electricity by means of a 
thermostat or some other device, as soon as the 
temperature of the room reaches a predetermined high 
level not exceeding 44°C, unless a higher temperature 
is required for an industrial process carried on in the 
air-conditioned enclosure. 

6.2.3 In case of air-conditioning plants where heating 
by means of an electric heater designed to operate in 
an air current is used, a safety device shall be 
incorporated in the installation to cut off the supply of 
electricity to the heating device whenever there is 
failure of the air current in which the heater is required 
to operate. Serious harm to the plant and sometimes 
fires may be caused by negligence in this respect. 

The surface temperature of all electric heaters used in 
an air-conditioned plant should be limited, preferably 
to 400°C, and in any case it shall not exceed 538°C, 
when measured in still air. 

6.2.4 Air-conditioning and ventilating systems 
circulating air to more than one floor or fire area shall 
be provided with dampers designed to close 
automatically in case of fire and thereby prevent 
spread of fire or smoke. Such system shall also be 
provided with automatic controls to stop fans in case 
of fire, unless arranged to remove smoke from a fire, 
in which case these shall be designed to remain in 
operation. 

6.2.5 Air-conditioning system serving large places of 
assembly (over 1 000 persons), large departmental 
stores or hotels with over 100 rooms in a single block 
shall be provided with effective means for preventing 
circulation of smoke through the system in the case of 
a fire in air filters or from other sources drawn into the 
system even though there is insufficient heat to actuate 
heat sensitive devices controlling fans or dampers. Such 
means shall consist of suitable photo-electric or other 
effective smoke sensitive controls, or may be manually 
operated controls. 

7 ELECTRICAL ASPECTS OF LIFTS AND 
ESCALATOR SERVICES 

7.0 General 

7.0.1 For the information of the electrical engineer, 
the lift/escalator manufacturer should advise the 
architect/engineer of the building of his structural and 
electrical requirements. This should be available early 
in the planning stage to ensure proper electrical 
provisions to be made for the service and suitable cables 
and switchgears. During preliminary planning of the 
building, the aspect of lifts and escalators installation 
shall be discussed with all concerned parties namely, 
client, architect, consulting engineer and/or lift 
manufacturer. 



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7,0.2 The following aspects shall be taken into account 
to decide the electrical requirements for lifts: 

a) Number of lifts, size, capacity and position; 

b) Number of floors served by the lift; 

c) Height between floor levels; 

d) Provisions for machine room and proper 
access to it; 

e) Provisions for ventilation and lighting; 

f) Electric supply required; 

g) Details of wiring and apparatus required; 
h) Quantity/quality of service; 

j) Occupant load factors; 

k) Car speed; 

m) Control system; 

n) Operation and maintenance; 

p) Provision for lift and depth; 

q) Number of entrances; 

r) Provision of telephone or alarm bell inside 
the lift car; 

s) Provision of battery backup emergency light 

inside the lift car; and 
t) Providing battery backup automatic rescue 

device or uninterrupted power supply (UPS). 

7.1 Design and Operation 

Reference is drawn to IS 14665 (Part 2/Sec 1), IS 14665 
(Part 2/Sec 2), IS 14665 (Part 3/Sec 1) and IS 14665 
(Part 3/Sec 2). 

7.2 Electrical Installation Requirements 

7.2.1 General 

The requirements for main switches and wiring with 
reference to relevant regulations may be adhered to. 
The lift maker should specify, on a schedule, particulars 
of full load current, starting current, maximum 
permissible voltage drop, size of switches and other 
details to suit requirements. For multiple lifts a diversity 
factor may be used to determine the cable size and 
should be stated by the lift manufacturer. 

It is important that the switches at the intake and in the 
machine room which are provided by the electrical 
contractor are of correct size, so that correctly rated 
fuses can be fitted. No form of 'No Volt' trip relay 
should be included anywhere in the power supply of 
the lift. 

The lift maker should provide overcurrent protection 
for power and control circuits, either on the controller 
or by a circuit-breaker, but the following are not 
included in the contract. 

a) Power supply mains — The lift sub-circuit 



from the intake room should be separate from 
other building service. 
Each lift should be capable of being isolated 
from the mains supply. This means of 
isolation should be lockable. 

b) For banks of interconnected lifts, a separate 
sub-circuit is required for the common 
supervisory system, in order that any car may 
be shut down without isolating the 
supervisory control of the remainder. 

c) Lighting — Machine rooms and all other 
rooms containing lift equipment should be 
provided with adequate illumination and with 
a switch fixed adjacent to the entrance. At least 
one socket outlet, suitable for lamps or tools, 
should be provided in each room. 

The car lighting supply should be independent of the 
power supply mains and should be connected to the 
inverter system with battery backup. 

Pits should be provided with a light, the switch for 
which should be in the lift well, and accessible from 
the lower terminal floor entrance. 

When the alarm system is connected to a transformer 
or trickle-charger, the supply should be taken from the 
machine room lighting. 

7.2.2 Electrical Wiring and Apparatus 

7.2.2.1 All electrical supply lines and apparatus in 
connection with the lift installation shall be so 
constructed and shall be so installed, protected, worked 
and maintained that there may be no danger to persons 
therefrom. 

7.2.2.2 All metal casings or metallic coverings 
containing or protecting any electric supply lines of 
apparatus shall be efficiently earthed. 

7.2.2.3 No bare conductor shall be used in any life car 
as may cause danger to persons. 

7.2.2.4 All cables and other wiring in connection with 
the lift installation shall be of suitable grade for the 
voltage at which these are intended to be worked and if 
metallic covering is used it shall be efficiently earthed. 

7.2.2.5 Suitable caution notice shall be affixed near 
every motor or other apparatus operating at a voltage 
exceeding 250 V. 

7.2.2.6 Circuits which supply current to the motor shall 
not be included in any twin or multicore trailing cable 
used in connection with the control and safety devices. 

7.2.2.7 A single trailing cable for lighting control and 
signal circuit shall be permitted, if all the conductors 
of this trailing cable are insulated for maximum voltage 
running through any one conductor of this cable. 



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7.2.2.8 Emergency signal or telephone 

It is recommended that lift car should be provided either 
with an emergency signal that is operative from the 
lift car and audible outside the lift well or with a 
telephone. 

When an alarm bell is to be provided, each car is fitted 
with an alarm push which is wired to a terminal box in 
the lift well at the ground floor by the lift maker. This 
alarm bell, to be supplied by the lift maker (with 
indicator for more than one lift), should be fixed in an 
agreed position and wired to the lift well. The supply 
may be from a battery (or transformer) fixed in the 
machine room or, when available, from the building 
fire alarm supply. 

When a telephone is to be provided in the lift car, the 
lift maker should fit the cabinet in the car and provide 
wiring from the car to a terminal box adjacent to the 
lift well. 

7.2.2.9 Building Management System — Interface for 
Lifts 

Where more than three lifts are provided in a building 
and especially when these are provided at different 
locations in the building, a form of central monitoring 
may be provided. Such central monitoring may be 
through a Building Management System, if provided 
in the building or through a display panel. 

7.2.2.10 Earthing 

The terminal for the earthing of the frame of the motor, 
the winding machine, the frame of the control panel, 
the cases and covers of the tappet switch and similar 
electric appliances which normally carry the main 
current shall be at least equivalent to a 10 mm diameter 
bolt, stud or screw. The cross -sectional area of copper 
earthing conductor shall be not smaller than those 
specified in Part 1/Sec 14 of the Code. 

The terminal for the earthing of the metallic cases and 
covers of doors interlocks, door contacts, call and 
control buttons, stop buttons, car switches, limit 
switches, junction boxes and similar electrical fittings 
which normally carry only the control current shall 
be, at least equivalent to a 5 mm brass screw, such 
terminal being specially provided for this purpose. 

The earthing conductor shall be secured to earthing 
terminal in accordance with the recommendations 
made in IS 3043 and also in conformity with the 
provisions of Indian Electricity Rules 1956. 

Where screwed conduit screws into electric fittings 
carrying control current and making the case and cover 
electrically continuous with the conduit, the earthing 
of the conduit may be considered to earth the fitting. 
Where flexible conduit is used for leading into a fitting, 



the fitting and such length of flexible conduit shall be 
effectively earthed. 

One side of the secondary winding of bell transformers 
and their cases shall be earthed. 

73 Additional Requirements for Escalators 

7.3.1 Connection Between Driving Machine and Main 
Drive Shaft 

The driving machine shall be connected to the main 
drive shaft by toothed gearing, a coupling, or a chain. 

7.3.2 Driving Motor 

An electric motor shall not drive more than one 
escalator. 

7.3.3 Brake 

Each escalator shall be provided with an electrically 
released, mechanically applied brake capable of 
stopping the up or down travelling escalator with any 
load up to rated load. This brake shall be located either 
on the driving machine or on the main drive shaft. 

Where a chain is used to connect the driving machine 
to the main drive shaft, a brake shall be provided on 
this shaft. It is not required that this brake be of the 
electrically released type, if an electrically released 
brake is provided on the driving machine. 

7.3.4 No bare conductor shall be used in any escalator 
as may cause danger to persons. 

7.3.5 Electrical conductors shall be encashed in rigid 
conduits, electrical tubings or wireways which shall 
be security fastened to the supporting structure. 

7.3.6 All electrical supply lines and apparatus in the 
escalator shall be of suitable construction and shall be 
so installed, protected, worked and maintained that 
there is no danger to persons from them. 

All metal casings or metallic coverings, containing or 
protecting any electric supply line or apparatus shall 
be efficiently connected with earth. 

7.3.7 Disconnect Switch 

An enclosed, fused switch or a circuit-breaker shall be 
installed and shall be connected into the power supply 
line to the driving machine motor. Disconnecting 
switches or circuit-breakers shall be of the manually 
closed multi-pole type. The switch shall be so placed 
that it is closed to and visible from the escalator 
machine to which the supply is controlled. 

With dc power supplies the main disconnecting switch 
and any circuit-breaker shall be so arranged and 
connected that the circuit of brake magnet coil is 
opened at the same time that the main circuit is opened. 



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73.8 Enclosure of Electrical Parts 

All electric safety switches and controllers shall be 
enclosed to protect against accidental contact. 

7.3.9 Caution Notice 

Suitable 'CAUTION' notice shall be affixed near every 
motor or other apparatus operating at a voltage 
exceeding 250 V. 

7.3.10 Insulation 

The electrical parts of starting and stopping devices, 
other operating and similar devices, controllers and 
similar other parts shall be efficiently insulated and 
the insulation shall be capable of withstanding for a 
period of one minute the continuous application of a 
ac test voltage equal to ten times the voltage at which 
these electrical parts are energized, subject to a 
maximum voltage of 2 000 V when the test voltage is 
applied between contacts or similar parts in the open 
position, and between such contacts and earthed parts. 

8 ELECTRICAL ASPECTS OF AUDIO SYSTEM 
SERVICES 

8.0 General 

8.0.1 This clause covers essential installation design 
aspects of electrical audio systems for indoor and 
outdoor use both for temporary and permanent 
installations. 

8.0.2 This applies to sound distribution systems and 
public address systems but does not cover installations 
in conference halls where both microphones and 
loudspeaker are distributed amongst the audience. 

8.0.3 Specific requirements if any, for individual 
occupancies are covered in individual Sections of the 
Code. 

8.0.4 For guidance on selection of equipment and their 
installation and maintenance, reference shall be made 
to IS 1881 and IS 1882. 

8.1 Exchange of Information 

8.1.1 The initial and ultimate requirements of the 
installations should be ascertained as accurately as 
possible by prior consultations. Plans shall show, 

a) details of the installation proposed, 

b) accommodation and location of the central 
amplifier equipment, and 

c) ducts and overhead lines required for wiring. 

8.2 Design Requirements 

8.2.0 The output from the microphone, gramophone, 
tape-recorder or radio receiver or CD player from a 
sound film is amplified and presented through a system 



of loudspeakers installed at chosen locations. The 
design of this installation shall be such that, depending 
on the nature of occupancy, the quality of reproduction 
is as desired. Reference is drawn to 5.2 of IS 1881 and 
IS 1882 on the quality of reproduction suitable for 
different purposes, and the acoustic power 
requirements therein. The choice of equipment such 
as these for input signals, amplifying equipment/system 
and loudspeaker shall be governed by the 
considerations enumerated in IS 1881 and IS 1882. 

8.2.1 Wiring for Audio System 

8.2.1.0 All equipments shall be securely installed in 
rooms guarded against unauthorized access. 
Precautions shall be taken to keep dust away. 

8.2.1.1 All present controls should be mounted behind 
cover plates and designed for adjustment only with the 
help of tools. All controls shall be mechanically and 
electrically noiseless. 

8.2.1.2 The positioning of equipment shall be such that 
the lengths of the interconnecting cables is kept to the 
minimum. 

8.2.1.3 In case the number of the equipment is large, they 
shall be mounted on racks of suitable dimensions of metal 
or wood, in such a manner that the controls are within 
easy reach. The patch cords shall be neatly arranged. 

8.2.1.4 In determining the positioning of the 
microphones and loudspeakers in the installation, 
advice of an acoustical expert shall be sought for best 
accuracy and reproducibility. 

8.2.1.5 For outdoor installations, the line-matching 
transformers shall be mounted in weather-proof 
junction boxes. 

8.2.1.6 In large open grounds such as an outdoor 
stadium, care shall be taken to ensure that the sound 
heard from different loudspeakers do not have any 
noticeable time lag. 

8.2.1.7 The plugs and sockets used in electrical audio 
systems shall not be interchangeable with those meant 
for power currents. 

8.2.1.8 Microphone and gramophone cables shall 
preferably use twisted pairs of conductors with 
sufficient insulation screened continuously with a close 
mesh of tinned-copper braid. The copper braiding 
should be sheathed with an insulating covering. These 
shall be isolated from power, loudspeaker and 
telephone cables. Joints in the cables shall be avoided. 
Microphone cables shall be laid without sharp bends. 
Indoor cables can be laid on the floor along the walls 
or under the carpet. When laid in the open, they shall 
be either buried in the ground at a depth not less than 
20 cm, or inside an iron-pipe at that depth if heavy 



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mechanical movement is expected above. This may 
also be laid overhead at a height not less than 3.5 m, 
clipped securely to a bearer wire. Any wiring required 
to be run along corridors or outside walls below 1.8 m 
shall be protected by a conduit. 

8.2.1.9 The loudspeaker cables shall be so chosen that 
the line losses do not exceed the values given in Table 1 
of IS 1882. 

8.2.2 Power Supplies 

8.2.2.1 The equipment should normally operate from 
230 V, single phase 50 Hz ac mains supply. A voltage 
regulating device shall be provided if the regulation is 
poorer than ±5 percent. In the absence of ac mains 
supply the system shall be suitable for operating from 
a storage battery. 

8.2.2.2 The supply mains shall be controlled by a MCB 
of adequate capacity. 

8.2.3 Earthing 

Proper earthing of the equipment shall be made in 
accordance with good practice. 

8.3 Inspection and Testing 

The completed installation shall be inspected and tested 
by the engineer to ensure that the work has been carried 
out in the manner specified. 

8.4 Miscellaneous Provisions 

Where necessary, that is in installations where the 
breakdown of the sound distribution systems should 
be restored instantaneously or within a limited time, 
the stand-by equipment shall be readily available. 

9 ELECTRICAL ASPECTS OF FIRE ALARM 
AND FIGHTING SYSTEMS 

9.0 General 

9.0.1 This clause covers the electrical aspects of the 
installation of fire alarm/protection system in buildings. 

9.0.2 This clause is applicable in general to all types 
of occupancies, while specific requirements if any or 
individual situations are covered in the respective 
sections of the Code. 

9.0.3 For total requirements for fire protection of 
buildings, including non-electrical aspects such as 
choice and disposition of fire-fighting equipment, 
depending on the nature of occupancy installation and 
maintenance aspects, etc., reference shall be made to 
SP 7 and the relevant Indian Standards. 

9.1 Fire Detectors 

9.1.1 The following types of fire detectors are available 
for installation in buildings: 



a) Heat detectors {see IS 2175): 

1) 'Point' or 'spot' type detector 

2) Line type detector. 

NOTE — These may be of fixed temperature 
detector or rate of rise detector. 

b) Smoke detectors: 

1) Optical detectors. 

2) Ionization chamber detector, 

3) Chemically sensitive detector. 

c) Flame detectors. 

9.1.2 For guidance on their choice and siting in the 
installation, see SP 7. 

9.2 Wiring for Fire Alarm Systems 

9.2.1 The equipment and wiring of the fire alarm system 
shall be independent of any other equipment or wiring, 
and shall be spaced at least 5 cm away from each other 
and other wiring. The wiring of the fire alarm systems, 
shall be in metallic conduits. The wiring shall be kept 
away from lift shafts, stair cases and other flue-like 
opening. 

9.2.2 Alarm sounders shall be of the same kind in a 
particular installation. 

9.2.3 For large or intricate premises, it is necessary 
that the origin of a call be indicated. For this, the 
premises shall be divided into sections zones. All call 
points in a section shall be connected to the same 
indicator. The various drops or lamp indicators shall 
be grouped together on the main indicator board or 
control panel. When the premises are extensive, a 
number of main indicator boards may be used covering 
different sectors. These shall be supplemented by sector 
indicators for the various sectors at a central control 
point. 

9.2.4 At the control point the indicator board or the 
zone and section indicating boards and all common 
control apparatus and supervisory equipment shall be 
located. For every installation a control point shall be 
provided, where it can be under constant observation. 
The main control centre shall be located on the ground 
floor and should be segregated from the rest of the 
building by fire-break wall. 

9.2.5 No section shall have more than 200 fire detectors 
connected together. 

9.2.6 The origin of the calls may be indicated by the 
use of lamp indicators. Each indicator shall include: 

a) two lamps connected in parallel associated 
with each indication, so arranged that failure 
of either of the lamps is readily apparent, or 

b) one lamp glowing during normal operation 
of the system for each section and the alarm 



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indicated by the extinguishing of the lamp for 
the section where the call originates. Alarms 
should not sound on the failure of the 
indicator. 

9.2.7 The arrangement of the circuits and the electrical 
connections shall be such that a call or fault in any 
circuit does not prevent the receipt of calls on any other 
circuit. 

9.2.8 The indicating device associated with the various 
call points and sections shall be grouped together on 
the main indicator board. If necessary remote indicating 
panel, with audible alarms in the night quarters of the 
caretaker of the building should be provided. 

9.2.9 The silencing switches/push buttons in their off 
position shall give an indication of this fact on the main 
control panel operation of silencing switches shall not 
prevent sounding of alarm from any other zone 
simultaneously, or cancel the other indications of the 
alarm or fault. 

9.2.10 For fire alarm systems, cables of the following 
types shall be used: 

a) Mineral insulated aluminium sheathed cables; 

b) PVC insulated cables, 

c) Rubber insulated braided cables, 

d) PVC or rubber insulated armoured cables, and 

e) Hand metal sheathed cables. 

The laying of the cables shall be done in accordance 
with Part 1/Section 1 of the Code. 

9.2.11 The source of supply for the alarm system shall 
be a secondary battery continuously trickle/float 
charged from ac mains, with facilities for automatic 
recharging in 8 h sufficiently to supply the maximum 
alarm load at an adequate voltage for at least 2 h. The 
capacity of battery shall be such that it is capable of 
maintaining the maximum alarm load on the system at 
an adequate voltage for at least 1 h plus the standing 
load or losses for at least 48 h. Suitable overload 
protective devices shall be provided to prevent 
discharging of the batteries through the charging 
equipment. 

9.3 Fire Fighting Equipment 

9.3.0 The choice of fire fighting equipment and their 
installation details shall be governed by the 
requirements specified in SP 7. 

9.3.1 Requirements for Electrical Drives for Pumps in 
Hydrant and Sprinkler Systems 

9.3.1.1 Full details of the electric supply shall be 
furnished together with details of generator plant to 
the appropriate authorities. 



9.3.1.2 Sufficient power shall be made available for 
the purpose and the power source shall be entirely 
independent of all other equipment in the premises and 
shall not be interrupted at any time by the main switch 
controlling supply to the premises. An indicator lamp 
shall continuously glow in a prominent position to 
indicate status of power in the substation and in the 
fire-pump room. 

9.3.1.3 Pumping sets shall be direct coupled type, and 
shall work satisfactorily at varying load. 

9.3.1.4 All motors and electrical equipment shall be 
continuously rated, drip-proof with air inlets and outlets 
protected with meshed wire panels where required 
motors shall have a suitable fixed warming resistance 
to maintain them in dry condition. 

9.3.1.5 The starting equipment of the set shall 
incorporate an ammeter and clearly marked to show 
full load current. They shall not incorporate no-volt 
trips. 

9.3.1.6 The electric circuit for fire fighting system shall 
be provided at its origin with a suitable switch for 
isolation, but overload and no- volt protection shall not 
be provided in the switch. 

10 ELECTRICAL CALL BELL SERVICES 

10.0 General 

10.0.1 Guidance on installation of electric bells and 
call systems are covered in IS 8884. 

10.0.2 On the basis of information collected on the 
extent of installation of electric bells and buzzers, or 
indicator call system in the building, the following 
aspects shall be ascertained in collaboration with the 
parties concerned: 

a) Accommodation required for control 
apparatus, location and distribution points; 
and 

b) Details of chases, ducts and conduits required 
for wiring. 

10.1 Equipment and Materials 

10.1.1 If wooden bases are used for bells and buzzers, 
the component parts shall be rigidly held together 
independently of the base, so that they are unaffected 
by any warping. 

10.1.2 Bells and buzzers which have a make or break 
contact shall be provided with means of adjusting the 
contact gap and pressure and means for locking the 
arrangement. 

10.1.3 Equipment for outdoor use shall be suitably 
protected against the environmental conditions. 



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10.1.4 Bell push switches shall be of robust 
construction. Terminals shall be of adequate size and 
should be so arranged that the loosening of a terminal 
screw does not disturb the contact assembly. Any 
flexible chords attached to them should be covered with 
hard wearing braid. 

10.1.4.1 Relays may be required for the following 
situations: 

a) Where mains operated device is to be 
controlled by a circuit operating at a voltage 
not exceeding 24 V, 

b) For repeating a call indication until at a distant 
point or points, and 

c) For maintaining a call indication until an 
indication is reset. 

10.1.5 The indications shall be one of the following 
types: 

a) Lamp type — where sound of bell is 
undesirable; for example in hospitals or in 
noisy locations such as forges, mills, etc. 

b) Flag type — where positive indication is 
required which remain in position until 
restored. 

c) Pendulum type — for small installations 
having up to 20 call points. 



10.2 Choice of Call Bell System 

The following guidelines are recommended: 

a) Simple call bell system — For dwellings and 
small offices (see Fig. 1). 

b) Multiple call bell system — Hotels, hospitals 
or similar large buildings where call points 
are numerous (see Fig. 2). 

c) Time bell system — Factories, schools. 

10.3 Power Supply 

The system may be operated at the normal mains 
voltage, though it is preferable for the control circuit 
to be operated at a voltage not exceeding 24 V. 

10.4 Wiring 

The wiring shall be done in accordance with 
Part 1/Section 9 of the Code. 

11 CLOCK SYSTEMS 

11.1 Design Considerations 

11.1.1 Reference is drawn to 5.1 of IS 8969. A 
schematic diagram is shown in Fig. 3. 

11.1.2 The enclosure of the clocks shall have no 
openings giving access to live parts or functional 




SUPPLY 

Fig. 1 Simple Electric Call Bell System 



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BELL PUSH 
SWITCHES 



^Hr 



BELL PUSH 
SWITCHES 



N s INDICATOR 



BELL PUSH 
SWITCHES 



tHt 



BELL PUSH 
SWITCHES 

INDICATOR 



BELLPU&H 
SWITCHES 



THif 



bHTpuSFT 

SWITCHES 



I V INDICATOR 



BELL PUSH 
SWITCHES 



tHt 



BELL PUSH 
SWITCHES 



N i INDICATOR 



SUPPLY 



z 



CENTRAL SWITCHROOM 
WITH FLOOR INDICATOR 



Fig. 2 Multiple Call Bell System 



insulated parts or functional insulation other than the 
openings necessary for the use and working of the 
clocks. Where such openings are necessary, sufficient 
protection against accidental contact with live parts 
shall be provided. 

11.1.3 To ensure necessary continuity of supply, direct 
connection of the system to the supply mains is not 
recommended. Batteries should always be provided. 
The capacity of the battery shall be at least sufficient 
to supply the installation for 48 h, not less than 10 Ah. 

11.1.3.1 Where the supply is ac, single battery on 
constant trickle charge is recommended, means being 
provided for charging at a higher rate when necessary. 

11.1.3.2 Where the supply is dc, two batteries should 
be provided with changeover switch. 



11.2 Location of Clocks 

11.2.1 The master clock shall be placed in a room not 
smaller than 2.4 m x 3.6 m. 

11.2.2 The location and size of slave clocks may 
frequently depend upon aesthetic requirements, but 
from the point of view of readability, a ratio of 
0.30 m diameter of dial to every 2.7 m of height is 
acceptable. The following is adequate: 



Dia of Clock 


Height from Floor 


0.30 m 


2.70 m 


0.45 m 


3.30 m 


0.60 m 


4.50 m 



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SP 30: 2011 



11.3 Wiring 

The wiring shall be done in accordance with Part 1/ 
Section 9 of the Code. Special conductor shall be 
provided, or the conduit may be colour coded for 
distinction from other circuits. 

12 ELECTRICAL ASPECTS OF COMPUTER 
CONTROL OF ENVIRONMENTAL SYSTEMS 

12.0 General 

12,0.1 Building users require services to meet the 
environmental and functional needs associated with a 
particular type of building, and these services vary 
considerably according to the type of building involved. 
However, the basic requirements are for comfort, safety 
security, efficiency, reliability and operational utilities. 
The increased application requirement calls for 
coordinated and efficient control of the various systems 
and their sub-systems. Configuration of these systems 
in a computer programme is a necessicity now. 

12.0.2 General building classifications are residential, 



commercial, industrial, public, medical establishments 
and industrial premises. The requirements differ 
according to the particular purpose of the building. The 
complexities of the services also relate to the 
requirements and additionally to the size and class- 
type of the building. 

12.1 Exchange of Information 

12.1.0 The architect should exchange information with 
the engineer concerned when the building plans are 
being prepared. The chief purpose of such an exchange 
is to obtain information regarding the architectural and 
electrical features of the building so that due provision 
may be made to retain the aesthetic features and the 
essential services while planning the locations of the 
various devices and equipment of the environmental 
services. Information may also be obtained at an early 
stage regarding other services, such as electrical 
installation, gas and water pipes etc. 

12.1.1 Scale drawings showing plans and elevations 
of the structure, electrical wirings shall be obtained 




AC SUPPLY 

Fig. 3 Impulse Master Clock System 



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and the nature and location of the devices, sensors and 
controllers of the environmental services shall be 
indicated on them. 

12.1.2 The initial and final requirements of the 
installations should be ascertained as accurately as 
possible by prior consultations. Plans shall show, 

a) details of the installations proposed; 

b) accommodation and locations of the central 
control units, server, monitor, etc; and 

c) ducts and cable routing required for wiring. 

12.2 Building Management System (BMS) 

12.2.0 Thermal comfort, lighting, ventilation, air- 
conditioning, security, safety, fire detection and control 
system and electrical power are always required, and 
residential building represents this basic level of need. 

12.2.1 The management of building services systems 
for a larger establishment is more difficult due to the 
variety, increased complexity, lack of individual 
responsibility and high capital and operating costs for 
the systems involved. The more complex control 
systems are termed building management systems 
(BMS). They are employed in commercial, public and 
industrial buildings and control the services of heating, 
ventilation, air-conditioning, steam, refrigeration, gas, 
water, general and emergency lighting, emergency 
electrical systems, power distribution, mechanical 
transportation, fire detection alarm and fighting 
systems, general and noxious fume ventilation, security 
and waste disposal. 

12.2.2 The building management systems (BMS) 
means that all services can be monitored and reset from 
a central location without delay or movement by the 
engineer. BMS can also advise on preventative 
maintenance schedules, thereby improving overall 
plant reliability and operating efficiency. Consequently, 
plant operation is greatly simplified by allowing an 
engineer to reset any control level, monitor energy con- 
sumption, organize maintenance and make fault 
diagnosis from a central location. Remedial action is 
quicker and can often be carried out by a smaller 
engineering staff than would be required otherwise. 

12.3 BMS Architecture 

12.3.1 BMS architecture and performance 
requirements shall be based on a distributed system of 
intelligent, stand alone controllers, operating BMS 
incorporates control and monitoring of all systems such 
as environmental, fire and security but, in some cases, 
separate dedicated fire protection systems are favoured 
by the authorities and reference to local fire codes and 
regulations is essential. The integration of fire 
protection and security systems into BMS shall be 



subject to the approval of the local fire prevention 
authority. It is possible to keep the fire protection 
system panel separate while still providing 
communication links with the BMS for alarm and 
reporting purposes. 

12.3.2 Back-up power supplies such as the UPS 
systems, although required for any BMS, need more 
consideration for centralized intelligence systems. A 
parallel systems structure and duplication of equipment 
to provide redundancy facilities may also be necessary, 
depending on the level of reliability required or the 
importance of the functions. 

12.4 Design Requirements 

12.4.1 The BMS shall include all workstation software 
and hardware, Process Control Units (PCU), Terminal 
Controllers, Local Controller, Local Area Network 
(LAN), sensors, control devices, actuators, system 
software, Interconnecting cable, installation and 
calibration, supervision, Distributed intelligence 
systems also have a central computer, with the addition 
of remote intelligent outstations capable of carrying 
out all control functions independent of the main 
computer. Outstations are located near to the building 
zone which they serve, as in the earlier systems, and 
are programmed to perform the required control 
functions. The outstation can, however, be interrogated 
and reset from the main computer and also 
communicate routine information and alarms as 
required by the plant operator. 

12.4.2 System administration shall be available from 
the Workstation in Control Room on Ethernet LAN 
(Local Area Network) WAN (Wide Area Network) in 
the system. The system specifically must have the 
capability to support multiple workstations, depending 
on complexity and magnitude of the services, 
connected on the LAN or WAN network at the same 
time. The building management system shall allow all 
connected workstations to function in a true multi-user, 
multi-tasking environment employing user-friendly 
Windows platform using TCP/IP Protocol or any other 
open protocol. 

12.4.3 The system architecture shall be capable of 
supporting single site and/or campuses as well as 
multiple sites located in different geographical 
locations. 

12.4.4 The system shall be capable of modular 
expansion without software upgrades or wiring 
revisions. 

12.5 General Characteristic of Software 

12.5.1 Software shall be modular in design for 
flexibility in expansion or revision of the system. 



PART 1 GENERAL AND COMMON ASPECTS 



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SP 30 : 2011 



12.5.2 The software shall include a General Purpose 
Operating System, which will be based on a user- 
friendly open platform. The architecture of the system, 
and the application software/firmware shall generally 
be compiled for faster execution speeds. 

12.6 Hardware Requirements 

12.6.0 The BMS consists of many subsystems and 
equipment, sensors and peripheral devices. However, 
the servers provide a single interface point for 
operations, maintenance and management analysis. 
Various subsystems and systems are connected to 
provide information on different parameters at different 
locations. 

12.6.1 The on-site operator workstation shall be user 
friendly, operator interface with the complete system. 
As an example, the requirements of a workstation 
equipment are given below: 

a) Workstation equivalent to Pentium-IV 1GHz 
or higher processor, 

b) 256 MB Random Access Memory, 

c) 40 GB Hard Disk or better, 

d) 3.5 IN, 1.44 MB Diskette Drive, 

e) Read/Write CD ROM 52X or Faster; 

f) Serial Port, 

g) Parallel Printer Port, 
h) USB Port, 

j) 19" SVG Colour Monitor, 

k) Colour Graphics Card with at least 6 MB 

RAM, 
m) 101 Keyboard, 
n) 3 button track ball with scroll wheel/optical 

mouse, 
p) 3COM Etherlink III with modem, and 
q) Printer. 

12.6.2 System Controllers 

It is desirable to monitor and/or control all points in 
the system through 'Intelligent' Distributed Control 
Units. Each Distributed Control Unit in the system shall 
contain its own microprocessor and memory with a 
minimum 300 h battery backup. Each distributed 
control unit shall be a completely independent stand- 
alone 'master' with its own hardware clock calendar 
and all firmware and software to maintain complete 
on an independent basis. 

12.6.2.1 Communication backbone 

12.6.2.2 The central computer communicates with the 
outstations through a standard interface and either a 
dedicated line, a leased line or a telephone switched 
line. Smaller systems on one site are usually connected 



using a twisted pair in either a ring, star or tree network. 

12.6.2.3 Optic fibre transmission is currently being 
installed and allows very fast and high bandwidth 
transmission. As BMS becomes more widely accepted, 
it is likely that system capacities will increase to a level 
that will make optic fibre technology an attractive 
proposition. 

12.6.2.4 For transmission distances within the building 
or site up to about 1.6 km, telephone lines are usually 
employed. The computer and outstations are connected 
to the telephone line via a modem, which converts the 
input signals to pulses which are transmittable on the 
telephone line, thus enabling information to be 
transmitted and received. 

12.6.2.5 In many cases, particularly for remote sites 
an autodial modem restricts the use and cost of 
telephone lines by automatically communicating only 
when required. Autodial modems are therefore used 
for large or multiple sites and the telephone lines are 
accessed through the existing telecom system. Modems 
generally operate over a range of speeds (baud rate) 
with generally increased cost for the higher speed, for 
example, 9 600 baud is now common. (1 baud = 1 bit/ 
second.) The baud rate is software set to suit the 
particular system, and some manufacturers use higher 
transmission rates for directly wired systems. 

12.6.2.6 Autodial communication with the computer 
can be either direct dialling by the operator, 
programmed down-loading of data at predetermined 
times, or priority alarm reports. 

12.6.2.7 It is advisable to have more than one line per 
station, one of which is dedicated to priority reporting 
and the other to routine reporting and monitoring. This 
allows each function to be effective without conflict 
with the other. 

12.6.3 Control Monitoring Stations 

12.6.3.1 A typical control monitoring station consists 
of a microcomputer, visual display unit (VDU), 
backing store and printer. One station is usually 
installed in a central location, but systems with several 
stations working on a master/slave principle can be 
obtained for large sites. 

12.6.3.2 Buildings under phased development can be 
provided with a distributed intelligence system without 
a central computer. Under these circumstances, the 
outstation can be programmed and interrogated directly 
by portable hand-held microcomputers, which are 
taken around the site by personnel and plugged into 
the outstation as required. A central computer can be 
added to the system at a later date, when the 
development is complete or finances allow. 



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12.6.33 The location of the central computer requires 
careful consideration and should be provided with a 
clean power supply with back-up, as referred to 
previously. If connected to fire safety systems, it should 
be located where it can be easily accessed and 
interrogated by the fire brigade. The fire alarm 
protection system may be connected directly to the fire 
brigade, but the information supplied at the control 
station is likely to be more comprehensive and useful 
for directing fire-fighting operations and controlling 
services that may affect safety or the spread of fire. 
Smoke removal and staircase pressurization systems 
for high rise buildings are often an integral part of the 
mechanical ventilation or air conditioning system. 
When this is the case, ready access by the fire brigade 
for system status and control is essential. 

12.6.4 VDUs and Key Boards 

12.6.4.1 High resolution VDUs enable text and 
graphics to be displayed. Communication with the 
system software can be through keyboard, mouse or 
touch screen. The touch screen is the simplest but least 
flexible method and has not been widely adopted by 
BMS manufacturers. 

12.6.5 Printers 

12.6.5.1 The output of data and information from the 
system is transferred to paper copy by a printer. This 
is essential so that a readable log of the system 
performance is available for distribution to other 
interested members of the engineering and 
management team. 

12.6.6 LANs 

12.6.6.1 The Controller LAN utilizes a peer-to-peer, 
token passing protocol to communicate between nodes 
on the network. The Process Control Unit shall provide 
direct control and monitoring of process functions from 
a Teer-to-Peer' LAN based controller. These process 
functions include environmental control, trending, 
energy management, and process control, which may 
be executed locally in a stand-alone mode or 
'globalized' across the Token Passing LAN, reports. 

12.6.7 Data Communications 

12.6.7.1 The standard specifications of generally 
acceptable ratings are indicated hereunder: 

a) PC port 

1 ) Protocol: Asynchronous, Polling, RS-232 

2) Baud Rate: 300, 1 200, 2 400 or 9 600 
Bps 

b) Host LAN 

1) Protocol: Token Passing, RS-485 

2) Baud Rate: 9 600 or 19 200 Bps 



c) Cables 



1) LAN 

22 AWG (0.324 mm) shielded, twisted 
pair (Belden 9184), 5 000' (1 500 mm) 
maximum or 24 AWG (0.206 mm) 
shielded, twisted pair (Belden 9841) 
4 000' (1200 mm) maximum per 
segment. 

2) Communication ports 

i) Controller LAN: RS-485; 19,200 or 
9 600 baud, SDLC, token-passing. 

ii) Hand Held Console Port: RJ11 
Modular, 1 200 baud, TTL. 

iii) RS-232 Port: PC @ 9 600 baud 
(7801 TAP function), or Hayes direct 
dial asynchronous modem @ 1 200, 
2 400 baud or 9 600 baud. 

iv) RS-232 Expansion Board Port: 
Supports synchronous modem, 
direct or two-way dial SDLC (78061 
or 78035 TAP functions) @ baud 
rates of 1 200 to 9 600 baud. 
Requires optional plug on module. 

3) Network wiring requirements 

Cable Supported: Twisted pair, shielded. 
22 AWG (0.324 mm 2 ) or larger, 30 pF/ft. 
or less between conductors, 55 pF/ft. or 
less conductor to shield, 85 to 150 Ohm 
impedance Belden 9841 or equivalent. 

4) Controller LAN length 

i) 1 500 m per segment, 
ii) 7 600 m with repeaters 

5) Controller LAN 

RS-485; 19 200 or 9 600 baud, SDLC, 
token-passing. 

6) Door controller LAN 

RS-485; 9 600 baud, asynchronous, 
polling. 

7) Hand held console port 

RJII Modular; 1 200 baud, TTL. 

8) RS-232 port 

PC @ 9 600 baud (7801 TAP function) 
or Hayes direct-dial a synchronous 
modem @ 1.200, 2 400 or 9 600 baud. 

9) RS-232 expansion board port 
Supports synchronous modem, direct or 
two-way dial SDLC (78061 or 78035 
TAP functions) @ baud rate of 1 200 to 
9 600 baud, Requires optional plug on 
module. 



PART 1 GENERAL AND COMMON ASPECTS 



123 



SP 30 : 2011 



10) Network wiring requirements 
i) Controller LAN length 

1 500 m per segment; 7 600 m with 

repeaters 
ii) Micro controller sub-LAN length 

1 500 m 

1) Cable supported 

Twisted pair, shielded, 22 AWG 
(0.324 mm 2 ) or larger, 30 pF/ft. 
or less between conductors, 55 
pF/ft. or less conductor to 
shield, 85 to 150 ohm 
impedance. 

2) Auto dial support telephone 
numbers 

8; stored in NOVRAM, Number 
of Digits — 31 per phone 
number; Supported — Phone, 
Beeper, Pager. 

12.6,8 Input/Output Sensors 

The input devices, depending on application and usage 
are: 

a) Space air temperature sensor, 

b) Relative humidity sensor, 

c) Air flow switch, 

d) Water flow switch, 

e) Water flow measuring transducer, 

f) Tank float switch, 

g) Current sensor, 
h) kWh transducer, 

j) Current, voltage and watt transducers, 

k) Occupancy sensor, 

m) Personal attendance sensor, 

n) Motion detector, 

p) Electronic door lock, 

q) Card reader, 

r) Access controller, 

s) Damper and valve and their actuators, and 

t) Electronic to pneumatic transducers. 

12.7 Installation 

All devices shall be installed in pre-engineering 
locations to be shown on the drawings in accordance 
with standard industry practice. 

12.7.1 Cables 

12.7.1.1 Cables in conduits 

It shall be secured from building structure, not from 
other services. 



12.7.1.2 Cables on trays and ladders 

Cables shall be fixed neatly to trays and ladders in 
single layers and parallel to the tray edge to avoid 
unnecessary crossovers. Cables shall be fixed at 
intervals not exceeding 48" by means of non-corrosive 
fastening materials. 

12.7.13 Segregation 

Data cabling shall be physically segregated from power 
and SMS input/output cabling and mains cabling. 

12.7 \1 Panels 

12.7.2.1 General 

Panels and Controllers shall be installed within a 
dedicated metal enclosure. 

12.7.2.2 Documentation 

Terminal numbers, points list, point addresses and short 
and long descriptions shall be described inside a plastic 
fade-free in a pocket. 

12.7.3 Small Point Controllers 

Small point controllers shall be installed adjacent to 
the controlled device, accessible for maintenance and 
contained in a suitable enclosure. 

12.7.4 Transmission Systems 

12.7.4.1 The BMS shall utilize the above LAN 
architecture to allow all of the Control Units to share 
data as well as to globalize alarms. The Controller LAN 
shall be based on a peer-to-peer, token passing 
technique with a data speed of not less than 19.2 kB. 
The turnaround time for a global point to be received 
by any node, including operator stations, shall be less 
than 3 s. 

12.7.4.2 Fiber Optic Pathways, Fiber Optic Media shall 
be used, as required, between buildings for the 
Controller LANs. Wherever the Optical Fiber enters 
or leaves the building, provide a fiber to hard copper 
interface device. The FOI shall regenerate data prior 
to transmitting this data to either the fiber or hard 
copper channels, so as not to result in the degradation 
of signal and to minimize the accumulation of errors 
between multiple FOIs. The FOI shall include ' 'jabber" 
protection, such that continuous data from a defective 
component will not destroy communications on the 
LAN. Provide visual indication of receiving and 
transmitting data activity on the hardwired drop. 
Provide visual indication of data transmission on the 
fiber media, jabber presence of fiber and hard copper 
channels, and bad signal quality on the hard copper 
channel. 



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12.8 Testing and Commissioning 

12.8.1 General 

The contractor shall perform all tests submitted in the 
Test Procedure and remain on site until the BMS is 
fully operational. 

12.8.2 Factory Testing 

Demonstrate such control loop shall be demonstrated 
including all calculations and global functions. Analog 
values shall be simulated, if required. Attendance by 
three (3) persons nominated by the Owner shall be 
allowed. After Test, summary of results and necessary 
modifications shall be submitted. 

12.8.3 Final Acceptance Test 

Acceptance of the system shall require a demonstration 
of the standby of the system. This test shall not start 
until the customer has obtained 30 days beneficial use 
of the system. 

13 TELEPHONE SYSTEMS 

13.0 General 

13.0.1 Telephone systems are classified as 
communications systems. Telephone communication 
through the public network is in most countries the 
responsibility of the Telecom administrations. These 
are systems, which must meet more stringent 
requirements for reliability of transmission. 

13.0.2 Electronic Private Automatic Branch Exchanges 
(EPABX) 

Electronic private branch exchanges are connected to 
the public exchanges through exchange lines. 
Operationally they form part of the subscriber 
equipment of the public telephone system. EPABX 
permit internal communication between the extensions 
of a system and external communication, for approved 
branch systems, over the exchange lines. 
Communication within the private branch system, 
normally, does not attract charges. 

13.0.3 Backbone Cabling 

Generally the inter-floor/inter-building backbone 
cabling is included in the scope of main building 
design. The backbone cabling should accommodate 
analog voice signal alone or analog and data signals 
simultaneously, as the case may be. It is the speed of 
data transmission and bandwidth, which matter most 
in the design of the communication backbone. 

13.1 Exchange of Information 

13.1.1 The exact requirement of the subscribers shall 
be assessed before drawing out the specification of the 



EPABX system. This means that information on 
number of subscribers in the building, distribution of 
the phones in the floors and other areas, nature of traffic 
etc are to be collected. 

13.1.2 The initial and final requirements of the 
installations should be ascertained as accurately as 
possible by prior consultations. Plans shall show: 

a) details of the installations proposed; 

b) the accommodation and location of the 
EPABX console, monitor, etc; and 

c) the ducts and cable routing required for 
wiring. 

13.2 Design Requirements 

13.2.1 The basic architecture and performance 
requirements of the modern day communication system 
is microprocessor-based pulse code modulated (PCM)/ 
Time Division Multiplexing (TDM) technology. 

13.2.2 The environmental conditions for the EPABX 
should preferably be controlled so that the room air 
temperature is maintained between 10 °C and 40 °C 
and relative humidity between 50 percent and 
95 percent. 

13.2.3 Integrated Services Digital Network (ISDN) is 
a common requirement now-a-days for commercial 
buildings since it is possible to handle simultaneous 
calls of different types namely voice, data and images 
transfer (Tele & Video conferencing) without any loss 
of data, at a minimum speed of 64 kBps, which can be 
increased further depending on requirement. EPABX 
system shall be capable of interfacing with other 
EPABX system through appropriate protocol. 

13.2.4 Hardware Requirement 

13.2.4.1 Electronic private automatic branch exchange 

In EPABX system the individual call stations are 
connected each by a twisted pair of wires to the 
automatic exchange (see Fig.4). This is also the 
termination for the exchange lines and, where 
necessary. 

13.2.4.2 Power supply 

Depending on the size and type of installation, the 
telephone system requires for its operation a dc power 
supply of 24 V or 48 V, which is obtained from the 
power mains through a rectifier. The rectifiers, provided 
with closed-loop control and for small and medium 
sized systems, are accommodated in the exchange 
housing. For large systems rectifiers (controlled) are 
supplied in separate cabinets. 

13.2.5 Standby Batteries 

Standby batteries can be provided as an adjunct to the 



PART 1 GENERAL AND COMMON ASPECTS 



125 



SP 30: 2011 



rectifier. These are necessary for important installations 
such as police stations, fire stations, etc, to cover 
possible main supply failures. 

13.2.6 Space Requirements 

13.2.6.1 The switching equipment for the telephone 
systems and small EPABX's takes up little room. Apart 
from the telephones, only relatively small wall- 
mounted junction boxes or exchange units are required. 
The exchanges, furthermore, produce little or no noise, 
so that they can be accommodated in an office if 
desired. For large systems a separate room should be 
provided for the exchange equipment, and similarly 
for the answering panel. Space should be allowed in 
planning for additional cabinets or racks, exchange 
equipment platforms etc that may be necessitated by 
future enlargement of the systems. The size of the 
battery room depends upon the type of power supply 
equipment used. 

13.2.7 Features 

There are various features available with the present 
day EPABX with introduction of concerned cards and 
features to be incorporated have to be decided 



depending on functional requirement. Some of the most 
common features included are Abbreviated Dialing, 
Recorded Announcement System, Last number redial, 
Executive override, multi-party conference, call 
forwarding, Direct Inward Dialing (DID), Automatic 
alarm make-up call, STD barring, group hunting, 
networking facility. 

13.3 Installation 

13.3.1 Wiring Installation 

For wiring within buildings, wire is mainly installed in 
embedded PVC conduit, or wiring cables with 
conductors of 0.6 mm or 0.8 mm diameter for surface 
wiring. 

13.3.1.1 In running the wires it is important to maintain 
a separation of at least 10 mm between the 
communications wiring and power cables. 

13.3.1.2 If conductors belonging to different 
communications systems are run together — for 
example, telephone wires and loudspeaker wires, or 
heavily loaded slave clock circuits — there is a risk of 
mutual interference between them. In such cases it is 
advisable to use screened cables. 



Building 1 



4th floor 



Branch lines 
o— 



Sub- distribution 
assembly 

3rd floor 



0) 

2nd floor -a 
as 

1st floor & 



Ground floor 



X 



Building 2 

X 



Building 3 



Conduit 



Main distribution 
assembly 



Basement 






Conduit 






Building distribution 
assembly 



X 



I 



Conduit 



Building distribution 
assembly 



o 3> 



126 



Main cable 

Fig. 4 Example of the Arrangement of a Basic EPABX System in Large Building 

NATIONAL ELECTRICAL CODE 



SF 30 : 2011 



13.3,1.3 In communication cables the cores are twisted 
together either in pairs or in star quad formation. For 
speech transmission — to avoid crosstalk — either a 
twisted pair or, in the case of the star quad a pair of 
opposite cores — should be used. 

13.3.2 Ducts, Apertures and Channels 

In the course of constructing the shell of the building the 
appropriate channels and ducts should be formed in the 
masonry and lead-through apertures provided in walls, 
ceilings, joists and pillars. Suitable accommodation should 
be provided for the distribution boards in large 
communications system (for example recesses, shafts 
etc). 

13.3.2.1 Conduits 

PVC conduit can be used for the individual sections of 
conduit networks in residential buildings for the riser 



conduit from floor to floor, horizontal branches in the 
floors up to the distribution boxes in the apartments, 
and between the distribution boxes in the apartments 
and the flush-type junction boxes. 

13.3.3 Connection of Telephones 

13.3.3.1 At the positions allocated for the telephones 
the conduit should be terminated in flush- type boxes. 
For junction boxes and socket outlets for the connection 
of telephones, flush-type boxes (switch boxes) to 
standards are adequate. A maximum of two telephones 
can be connected to a junction box. 

13.3.3.2 In most cases the telephone is connected 
permanently to the subscriber's line through a junction 
box. If it is required to be able to use it in a number of 
rooms, socket outlets and plugs should be provided. 
Units for flush and surface mounting are available for 
both methods of connection. 



3rd floor 




tr 








Plastic conduit 








— 16 mm conduit 


Flush 1 
connection jox y 




Distribution 




network to call 
station 










box 










2nd floor 
























Flush 
distribution box 




PI a clip ro- 


II 












nduit 23 mm 


Branch conauit 








1st floor 
























IP" 




Plastic co- 
nduit 29 mm 


II 




















Ground floor 












Conduit network 
to several call 








l~ 








stations 
(e.g. shops) 


















Ground floor or basement 








Riser conduit 










Distribution box 
for cable connection 













U' 



Cable 

Fig. 5 Typical Conduit Wiring System 
PART 1 GENERAL AND COMMON ASPECTS 



127 



SP 30: 2011 



13.3.4 Installation of Telephone Wiring 

13.3.4.1 Wiring in residential building 

In residential buildings a concealed wiring arrangement 
is most conveniently and economically installed in an 
adequately dimensioned conduit network. It has been 
found satisfactory to provide riser conduits or cable 
ducts and horizontal branch conduits to the apartments, 
with distribution boxes at the junctions (Fig. 5). With 
a concealed installation of this kind it is possible at 
any time to alter the wiring or add to it without 
inconvenience to the occupier. 

13.3.4.2 Wiring in non-residential buildings 

In office buildings, manufacturing plants, department 
stores etc. particular importance is attached to flexible 
arrangement and utilisation of the accommodation. To 
this end the, communication wiring can be run in 
underfloor trunking systems or window-sealed 
trunking rather than on the walls. 

13.3.5 Accessory Installation 

13.3.5.1 Main distribution board 

All the lines are collected in the main distribution board. 
The main distribution board should be located in the 
same part of the building in the immediate vicinity of 
the telephone equipment. If the telephone equipment 
extends over several buildings, each building is 
connected to the main distribution board by a main 
cable. 

13.3.5.2 Floor distribution board 

The floor distribution boards should be accommodated 
close to the stair well. The rising mains are run 
vertically to the floors. 

13.3.5.3 Preventive fire precautions (for example 
fireproof barriers) should be considered at an early 
stage of planning 

13.3.5.4 Riser cables 

The ducts and ceiling apertures for the riser cables 
should be sufficiently large to permit the later addition 
of cables or PVC conduits without great expense. 

13.3.5.5 Spare conduits 

In addition at least one extra conduit should be provided 
from one floor distribution board to the next. 

13.4 Inspection and Testing 

13.4.1 The completed installation shall be inspected 
and simulation testing to be done to ensure that all the 
designed functions are available as per the standards 
and norms of specified by the manufacturer. 



14 SUPPLIES FOR SAFETY SERVICES 

14.0 General 

14.0.1 For a safety service, a source of supply shall be 
selected which will maintain a supply of adequate 
duration. 

14.0.2 For a safety service required to operate in fire 
conditions, all equipment shall be provided, either by 
construction or by erection, with protection providing 
fire resistance of adequate duration. 

14.0.3 A protective measure against indirect contact 
without automatic disconnection at the first fault is 
preferred. In an IT system, continuous insulation 
monitoring shall be provided to give audible and visible 
indications of a first fault. 

14.0.4 Equipment shall be arranged to facilitate 
periodic inspection, testing and maintenance. 

14.1 Sources 

14.1.1 A source for safety services shall be one of the 
following: 

a) A primary cell or cells. 

b) A storage battery. 

c) A generator set capable of independent 
operation. 

d) A separate feeder effectively independent of 
the normal feeder (provided that an 
assessment is made that the two supplies are 
unlikely to fail concurrently). 

14.1.2 A source for a safety service shall be installed 
as fixed equipment and in such a manner that it cannot 
be adversely affected by failure of the normal source. 

14.1.3 A source for a safety service shall be placed in 
a suitable location and be accessible only to skilled or 
instructed persons. 

14.1.4 A single source for a safety service shall not be 
used for another purpose. However, where more than 
one source is available, such sources may supply stand- 
by systems provided that, in the event of failure of one 
source, the energy remaining available will be sufficient 
for the starting and operation of all safety services; 
this generally necessitates the automatic off-loading 
of equipment not providing safety services. 

14.1.5 Clauses 14,1,3 and 14.1.4 do not apply to 
equipment individually supplied by a self-contained 
battery. 

14.1.6 The location of the source shall be properly and 
adequately ventilated so that any exhaust gases, smoke 
or fumes from the source cannot penetrate, to a 
hazardous extent, areas occupied by persons. 



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14.2 Circuits 

14.2.1 The circuit of a safety service shall be 
independent of any other circuit and an electrical fault 
or any intervention or modification in one system shall 
not affect the correct functioning of the other. 

14.2.2 The circuit of a safety service shall not pass 
through any location exposed to abnormal fire risk unless 
the wiring system used is adequately fire resistant. 

14.23 The protection against overload in the circuit 
may be omitted. 

14.2.4 Every over-current protective device shall be 
selected and erected so as to avoid an over-current in 
one circuit impairing the correct operation of any other 
safety services circuit. 

14.2.5 Switchgear and control gear shall be clearly 
identified and grouped in locations accessible only to 
skilled or instructed persons. 

14.2.6 Every alarm, indication and control device shall 
be clearly identified. 

14.3 Utilization Equipment 

14.3.1 In equipment supplied by two different circuits, 



a fault occurring in one circuit shall not impair the 
protection against electric shock nor the correct 
operation of the other circuit. 

14.4 Special Requirements for Safety Services 
Having Sources not Capable of Operation in 

Parallel 

14.4.1 Precautions shall be taken to prevent the 
paralleling of the sources, for example by both 
mechanical and electrical interlocking. 

14.4.2 The requirements of the regulations for 
protection against fault current and against indirect 
contact shall be met for each source. 

14.5 Special Requirements for Safety Services 
Having Sources Capable of Operation in Parallel 

14.5.1 The requirements of the regulations for 
protection against short-circuit and indirect contact 
shall be met whether the installation is supplied by 
either of the two sources or by both in parallel. 

14.5.2 Precautions shall be taken, where necessary, to 
limit current circulation, particularly thereof third 
harmonics or multiples thereof, in the connection 
between the neutral points of sources. 



IS No. 

1881 : 1998 

1882 : 1993 
2175 : 1988 



2440 : 1975 
3103 : 1975 

3043 : 1987 
3362 : 1977 

3646 (Part 1): 1992 



7662 (Part 1): 1974 



8884 : 1978 



ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS RELATED TO BUILDING SERVICES 
Title IS No. Title 



Code of practice for indoor instal- 
lation of public address systems 
Code of practice for outdoor instal- 
lation of public address system 
Specification for heat sensitive 
fire detectors for use in automatic 
fire alarm system 
Guide for day lighting of buildings 
Code of practice for industrial 
ventilation 

Code of practice for earthing 
Code of practice for natural 
ventilation of residential buildings 
Code of practice for interior 
illumination: Part 1 General 
requirements and recommenda- 
tions for welding interiors 
Recommendations for orientation 
of buildings: Part 1 Non-industrial 
buildings 

Code of practice for the installation 
of electric bells and call system 



8969 : 1978 



14665 (Part 2/ 
Sec 1) : 2000 



14665 (Part 2/ 
Sec 2) : 2000 



14665 (Part 3/ 
Sec 1) : 2000 

14665 (Part 3/ 
Sec 2) : 2000 

SP 7 : 2005 
SP 72: 2010 



Code of practice for installation 
and maintenance of impulse and 
electronic master and slave 
electric clock systems 
Electric traction lifts: Part 2 
Code of practice for installation, 
operation and maintenance, 
Section 1 Passenger and goods 
lifts 

Electric traction lifts: Part 2 
Code of practice for installation, 
operation and maintenance, 
Section 2 Service lifts 
Electric traction lifts: Part 3 
Safety rules, Section 1 Passenger 
and goods lifts 

Electric traction lifts: Part 3 
Safety rules, Section 2 Service 
lifts 

National Building Code of India 
National Lighting Code 



PART 1 GENERAL AND COMMON ASPECTS 



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SECTION 12 SELECTION OF EQUIPMENT 



FOREWORD 

Several Indian Standards exist, which cover details of 
selection, installation, and maintenance of electric 
power equipment. This Part 1/Section 12 of the Code 
is formulated in such a manner as to bring out only the 
essential criteria for selection of equipment, and users 
of the Code are recommended to make reference to 
individual product codes for detailed guidelines. 

1 SCOPE 

This Part 1/Section 12 of the Code covers general 
criteria for selection of equipment. 

NOTE — This Part 1/Section 12 shall be read in conjunction 
with the Indian Standard/Codes on individual equipment. 

2 SELECTION OF EQUIPMENT 

2.1 Conformity to Indian Standards 

Every item of electrical equipment used in the 
installation shall conform to the relevant Indian 
Standards, wherever available. 

2.2 Characteristics 

Every item of electrical equipment selected shall have 
suitable characteristics appropriate to the values and 
conditions on which the design of the electrical 
installation (see 3.2 of Part 1/Section 7) is based and 
shall, in particular, fulfill the requirements given 
to 2.2.1 to 2.2.4. 

2.2.1 Voltage 

Electrical equipment shall be suitable with respect to 
the maximum steady voltage (rms value for ac) likely 
to be applied, as well as overvoltages likely to occur. 

NOTE — For certain equipment, it may be necessary to take 
account of the lowest voltage likely to occur. 

2.2.2 Current 

All electrical equipment shall be selected with respect 
to the maximum steady current (rms value for ac) 
which it has to carry in normal service, and with respect 
to the current likely to be carried in abnormal 
conditions and the period (for example, operating time 



of protective devices, if any) during which it may be 
expected to flow. 

2.2.3 Frequency 

If frequency has an influence on the characteristics of 
electrical equipment, the rated frequency of the 
equipment shall correspond to the frequency likely to 
occur in the circuit. 

2.2.4 Power 

All electrical equipment to be selected on the basis of 
its power characteristics, shall be suitable for the duty 
demanded of the equipment, taking into account the 
load factor and the normal service conditions. 

2.3 Conditions of Installation 

All electrical equipment shall be selected so as to 
withstand safely the stresses and the environmental 
conditions (see 3.2 of Part 1/Section 7 of this Code) 
characteristic of its location to which it may be exposed. 
The general characteristics of building installations are 
assessed according to the guidelines given in Part 1/ 
Section 8 of this Code. If, however, an item of 
equipment does not have by design the properties 
corresponding to its location it may be used on 
condition that adequate additional protection provided 
as part of the completed electrical installation. 

2.4 Prevention of Harmful Effects 

All electrical equipment shall be selected so that it will 
not cause harmful effects on, other equipment or impair 
the supply during normal service including switching 
operations. In this context, the factors which may have 
an influence include; 

a) Power factor, 

b) Inrush current, 

c) Asymmetrical load, and 

d) Harmonics. 

2.5 Guidelines on the selection of specific equipment 
are covered in the relevant Indian Standards. Guidelines 
on selection of protective devices are given at Part 1/ 
Section 14 of this Code. 



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SECTION 13 ERECTION AND PRE-COMISSIONING TESTING 

OF INSTALLATION 



FOREWORD 

Testing and ensuring that the installation conforms to 
the predetermined conditions before the installation 
could be energized, is a necessary prerequisite under 
the statutory provisions. Several aspects/parameters are 
required to be verified before an installation could be 
certified as ready for energizing and use. 

While a general check list of items to be checked and 
necessary tests to be done are included in this Section, 
individual product standards and individual Codes of 
practice cover more detailed guidelines on 
pre~commissioning checks for individual equipment. 

In addition to initial testing, periodic testing and 
preventive maintenance checks are necessary, the 
nature and frequency of such measures depending on 
the nature of the electrical installation in question. 
Guidelines on such aspects are outside the purview of 
the Code. However, a reference could be made to 
individual equipment codes which cover maintenance 
schedules. 

1 SCOPE 

This Part 1/Section 13 of the Code covers general 
principles of erection of installation and guidelines on 
initial testing before commissioning. 

2 REFERENCES 

A list of relevant Indian Standards is given at 
Annex A. 

3 ERECTION 

3.1 For the erection of the electrical installation, good 
workmanship by suitably qualified personnel and the 
use of proper materials shall be ensured. 

3.2 The characteristics of the electrical equipment, as 
determined in accordance with Part 1/Section 12 shall 
not be impaired in the process of erection. 

3.3 Protective conductors and neutral conductors shall 
be identifiable at least at their terminations by colouring 
or other means. These conductors in flexible cords or 
flexible cables shall be identifiable by colouring or 
other means throughout their length (see 3.6 of 
Part 1/Section 4). 

3.4 Connections between conductors and between 
conductors and other electrical equipment shall be 
made in such a way that safe and reliable contacts are 
ensured. For electrical wiring installation, IS 732 
should be followed. Also see Part 1/Section 14 of the 
Code. 



3.5 All electrical equipment shall be installed in such 
a manner that the designed cooling conditions are not 
impaired. 

3.6 All electrical equipment likely to cause high 
temperatures or electric arcs shall be placed or guarded 
so as to eliminate the risk of ignition of flammable 
materials. Where the temperature of any exposed parts 
of electrical equipment is likely to cause injury to 
persons, these parts shall be so located as to prevent 
accidental contact therewith. 

3.7 Several Indian Standards exist on installation of 
specific electrical equipment. These shall be adhered 
to during erection of the installation. 

4 INSPECTION AND TESTING 

4.1 Genera! Requirements 

4.1.1 Before the completed installation, or an addition 
to the existing installation, is put into service, inspection 
and testing shall be carried out in accordance with the 
Indian Electricity Rules, 1956. In the event of defects 
being found, these shall be rectified, as soon as 
practicable, and the installation retested. 

4.1.2 After putting the installation into service periodic 
inspection and testing shall be carried out in order to 
maintain the installation in a sound condition. 

4.1.3 Where an addition is to be made to the fixed 
wiring of an existing installation the latter shall be 
examined for compliance with recommendations of 
this Code. 

4.2 Inspection of the Installation 

4.2.0 General 

At the completion of wiring, a general inspection shall 
be carried out by competent personnel to verify that 
the provisions of this Code and that of Indian Electricity 
Rules, 1956 have been complied with. This, among 
other things, shall include checking whether all 
equipment, fittings, accessories, wires and cables, used 
in the installation are of adequate rating and quality to 
meet the requirements of the load. General 
workmanship of the electrical wiring with regard to 
the layout and finish shall be examined for neatness 
that would facilitate easy identification of circuits of 
the system, adequacy of clearances, soundness of 
termination with respect to tightness, contact pressure 
and contact area. A complete check shall also be made 
of all the protective devices, with respect to the rating, 
range of settings and for co-ordination between the 
various protective devices. 



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4.2,1 Substation Installations 

In substation installation it shall be checked whether, 

1) the installation has been carried out in 
accordance with the approved drawings; 

2) phase-to-phase and phase-to-earth clearances 
are provided as required; 

3) all equipments are efficiently earthed and 
properly connected to the required number 
of earth electrodes; 

4) the required ground clearance to live terminals 
is provided; 

5) suitable fencing is provided with gate with 
lockable arrangements; 

6) the required number of caution boards, fire- 
fighting equipments, operating rods, rubber 
mats, etc, are kept in the substation; 

7) in case of indoor substation, sufficient 
ventilation and draining arrangements are 
made; 

8) all cable trenches are provided with non- 
flammable covers; 

9) free accessibility is provided for all equipment 
for normal operation; 

10) all name-plates are fixed and the equipment 
are fully painted; 

11) all construction materials and temporary 
connections are removed; 

12) oil levels, bus bar tightness, transformer tap 
position, etc, are in order; 

13) earth pipe troughs and cover slabs are 
provided for earth electrodes/earth pits. 
Neutral and lightning arrester earth pits are 
marked for easy identification; 

14) earth electrodes are of GI pipes or CI pipes or 
MS rods or copper plates. For earth 
connections, brass bolts and nuts with lead 
washers are provided in the pipes/plates; 

15) earth pipe troughs, oil sumps/pits are free 
from rubbish and dirt and stone jelly and the 
earth connections are visible and easily 
accessible; 

16) Panels and switchgears are all vermin and 
damp proof and all unused openings or holes 
are blocked properly; 

17) the earth bus bars for tightness and for 
corrosion free joint surface; 

18) control switchfuses are provided at an 
accessible height from ground; 

19) adequate head room is available in the 
transformer room for easy topping up of oil, 
maintenance, etc; 

20) safety devices, horizontal and vertical 



barriers, bus bar covers/shrouds, automatic 
safety shutters/doors interlock, handle 
interlock for safe and reliable operation in all 
panels and cubicles; 

21) clearances in the front, rear and sides of the 
switchboards, are adequate; 

22) the gap in the horngap fuse and the size of 
fuse adequate; 

23) the switch operates freely, all the blades make 
contact at the same time. The arcing horns 
contact in advance, and the handles are 
provided with locking arrangements; 

24) Insulators are free from cracks, and are clean; 

25) in the case of transformers, there is any oil leak; 

26) connections to bushings in transformers are 
tightened and have good contact; 

27) bushings are free from cracks and are clean; 

28) accessories of transformers like breathers, 
vent pipe, buchholz relay, etc, are in order; 

29) connections to gas relay in transformers are 
in order; 

30) oil and winding temperature are set for 
specific requirements in transformers; 

31) in case of cable cellars, adequate 
arrangements to pump out water that has 
entered due to seepage or other reason is 
provided; and 

32) all incoming and outgoing circuits of panels 
are clearly and indelibly labelled for 
identifications both at the front and at the rear. 

4.2.2 Installation at Voltage not exceeding 650 V 

It shall be checked whether: 

a) all blocking materials that are used for safe 
transportation in switchgears, contractors, 
relays, etc, are removed; 

b) all connections to the earthing system are 
feasible for periodical inspection; 

c) sharp cable bends are avoided and cables are 
taken in a smooth manner in the trenches or 
alongside the walls and ceilings using suitable 
support clamps at regular intervals; 

d) suitable linked switch or circuit-breaker or 
lockable push button is provided near the 
motors/apparatus for controlling supply to the 
motor apparatus in any easily accessible 
location; 

e) two separate and distinct earth connections 
are provided for the motor apparatus; 

f) control switchfuse is provided at an accessible 
height from ground for controlling supply to 
overhead travelling crane hoists, overhead bus 
bar trunking; 



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g) the metal rails on which the crane travels are 
electrically continuous and earthed and 
bonding of rails and earthing at both ends are 
done; 

h) four core cables are used for overhead 
travelling crane and portable equipments, the 
fourth core being used for earthing, and 
separate supply for lighting circuit is taken; 

j) if flexible metallic house is used for wiring 
to motors and equipments, the wiring is 
enclosed to the full lengths, and the hose 
secured properly; 

k) the cables are not taken through areas where 
they are likely to be damaged or chemically 
affected; 

m) the screens and armours of the cables are 
earthed properly; 

n) the belts of the belt driven equipments are 

properly guarded; 
p) adequate precautions are taken to ensure that 

no live parts are so exposed as to cause danger; 
q) ammeters and voltmeters are tested and 

calibrated; 

r) the relays are inspected visually by moving 

covers for deposits or dusts or other foreign 

matter; 
s) flat washers backed up by spiring washers are 

used for making end connections; and 
t) number of wires in a conduit conform to 

provisions of this Code. 

43 Testing of Installation 

4.3.0 General 

After inspection, the following tests shall be carried 
out, before an installation or an addition to the existing 
installation is put into service, any testing of the 
electrical installation in an already existing installation 
shall commence after obtaining permit to work from 
the engineer-in-charge and after ensuring the safety 
provisions. 

4.3.1 Switchboards 

Switchboards shall be tested in the manner indicated 
below: 

a) all switchboards shall be tested for di-electric 
test in the manner recommended in IS 8623 
(Part 1), 

b) all earth connections shall be checked for 
continuity, 

c) the operation of all protective devices shall 
be tested by means of secondary or primary 
injection tests, 



d) the operation of the circuit-breakers shall be 
tested from all control stations, 

e) indication/signalling lamps shall be checked 
for working, 

f) the operation of the circuit-breakers shall be 
tested for all interlock, 

g) the closing and opening timings of the circuit- 
breakers shall be tested wherever required for 
autotransfer schemes, 

h) contact resistance of main and isolator 
contacts shall be measured, and 

j) the specific gravity of the electrolyte and the 
voltage of the control battery shall be 
measured. 

4.3.2 Transformers 

All commissioning tests as listed in IS 10028 (Part 2) 
shall be carried out. 

4.3.3 Cables 

Cable installations shall be checked as laid down in 
IS 1255. 

4.3.4 Motors and Other Equipment 

The following tests are made on motor and other 
equipment: 

a) The insulation resistance of each phase 
winding against the frame and between the 
windings shall be measured. Megohm-meter 
of 500 V or 1 000 V rating shall be used. Star 
points should be disconnected. Minimum 
acceptable value of the insulation resistance 
varies with the rated power and the rated 
voltage of the motor. 

The following relation may serve as a 
reasonable guide: 



*i=- 



20x£ n 
1000 -f IP 



where 

R x - insulation resistance in MQ at 25°C, 
E n = rated phase-to-phase voltage, and 
P = rated power kW. 

If the resistance is measured at a temperature 
different from 25°C, the value shall be 
corrected to 25°C. 
b) The insulation resistance as measured at 
ambient temperature does not always give a 
reliable value, since moisture might have been 
absorbed during shipment and storage. When 
the temperature of such a motor is raised, the 
insulation resistance will initially drop 



PART 1 GENERAL AND COMMON ASPECTS 



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considerably, even below the acceptable 
minimum. If any suspicion exists on this 
score, motor winding shall be dried out. 

4.3.5 Energymeters 

IS 15707 should be followed in case of energymeters, 

4.3.6 Wiring Installation 

The following tests shall be done: 

a) The insulation resistance shall be measured by 
applying between earth and the whole system 
of conductor or any section thereof with all 
fuses in place and all switches closed, and 
except in earthed concentric wiring, all lamps 
in position or both poles of installation 
otherwise electrically connected together, a dc 
voltage of not less than twice the working 
voltage, provided that it does not exceed 500 V 
for medium voltage circuits . Where the supply 
is derived from three-wire (ac or dc) or a 
polyphase system the neutral pole of which is 
connected to earth either direct or through 
added resistance, the working voltage shall be 
deemed to be that which is maintained between 
the outer or phase conductor and the neutral. 

b) The insulation resistance in megohms of an 
installation measured as in (a) shall be not less 
than 50 divided by the number of points on 
the circuits, provided that the whole 
installation need not be required to have an 
insulation resistance greater than 1MQ. 

c) Control rheostats, heating and power 
appliances and electric signs, may, if desired, 
he disconnected from the circuit during the 
test, but in that event the insulation resistance 
between the case or framework, and all live 
parts of each rheostat, appliance and sign shall 



be not less than that specified in the relevant 
Indian Standard or where there is no such 
specification shall be not less than 0.5 MQ. 

d) The insulation resistance shall also be 
measured between all conductors connected 
to one pole or phase conductor of the supply 
and all the conductors connected to the middle 
wire to the neutral on to the other pole of phase 
conductors of the supply. Such a test shall be 
made after removing all metallic connections 
between the two poles of the installation and 
in these circumstances the insulation 
resistance between conductors of the 
installation shall be not less than that specified 
in(b). 

e) On completion of an electrical installation (or 
an extension to an installation) a certificate 
shall be furnished by the contractor, 
countersigned by the certified supervisor 
under whose direct supervision the 
installation was carried out. this certificate 
shall be in a prescribed form as required by 
the local electric supply authority. 

4.3.7 Earthing 

For checking the efficiency of earthing the following 
tests are recommended (see IS 3043): 

a) The earth resistance of each electrode is 
measured. 

b) The earth resistance of earthing grid is 
measured. 

c) All electrodes are connected to the grid and 
the earth resistance of the entire earthing 
system is measured. 

These tests shall preferably be done during the summer 
months. 



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ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS ON INSTALLATION 



IS No. 
732 : 1989 

1255 : 1983 
1646 : 1997 



3043 : 1987 
4051 : 1967 



5571 : 2000 

8623 (Part 1) : 1993/ 
IEC 60439-1: 
1985 



Title IS No. 

Code of practice for electrical 

wiring installations 

Code of practice for installation 10028 (Part 2) : 

and maintenance of power 1981 

cables upto and including 33 kV 

rating 14927 

Code of practice for fire safety of 

buildings (general): Electrical (Part 1) : 2001 

installations (Part 2) : 2001 

Code of practice for earthing 

Code of practice for installation 

and maintenance of electrical 14930 

equipment in mines 

Guide for selection of electrical (Part 1) : 2001 

equipment for hazardous areas (Part 2) : 2001 

Specification for low-voltage 

switchgear and controlgear 

assemblies: Part 1 Requirements 15707 : 2006 



Title 

for type-tested and partially type- 
tested assemblies 
Code of practice for selection, 
installation and maintenance of 
transformers: Part 2 Installation 
Cable trunking and ducting 
systems for electrical installations : 
General requirements 
Cable trunking and ducting 
systems intended for mounting on 
walls or ceilings 

Conduit systems for electrical 
installations: 
General requirements 
Particular requirements — 
Conduit systems buried 
underground 

Testing, evaluation, installation 
and maintenance of ac electricity 
meters — Code of practice 



PART 1 GENERAL AND COMMON ASPECTS 



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SECTION 14 EARTHING 



FOREWORD 

Earthing provides safety of persons and apparatus 
against earth faults. Any system is characterised by 
the type of distribution system, which include types of 
systems of live conductors and types of system 
earthing. The different types of earthing systems are 
also covered under this Part 1/Section 14 of the Code. 
The choice of one system or the other would depend 
on several considerations as each offer different degree 
of performance/safety. 

This Part 1/Section 14 of the Code summarises the 
essential requirements associated with earthing in 
electrical installations. These relate to general conditions 
of soil resistivity, design parameters of earth electrode, 
earth bus and earth wires and methods of measurements. 
Particular requirements for earthing depending on the 
type of installation are covered in respective Sections of 
the Code. 

1 SCOPE 

This Part 1/Section 14 of the Code covers general 
requirements associated with earthing in electrical 
installations. Specific requirements for earthing in 
individual installations are covered in respective Parts 
of the Code. 

NOTES 

1 This Section shall be read in conjunction with the provisions 
of IS 3043. 

2 Additional rules applying to earth leakage circuit-breaker 
systems are covered in Annex A. 

2 REFERENCES 

For further details, the following standards may be 
referred: 



3 GENERAL REMARKS 



3.0 General 



IS No. 
732 : 1989 

3043 : 1987 

IS 8437(Part 1) : 
1993 

IS 8437(Part 2) : 
1993 

IS/IEC 60947-2 : 

2006 
IS/IEC 60947-4-1: 

2002 



Title 

Code of practice for electrical 
wiring installations (third revision) 
Code of practice for earthing (first 
revision) 

Guide on effects of current passing 
through human body: Part 1 
General aspects 

Guide on effects of current passing 
through human body: Part 2 
Special aspects 

Low voltage switchgear and 
controlgear: Part 2 Circuit breakers 
Low-voltage switchgear and 
controlgear: Part 4 Contactors and 
motor-starters, Section 1 Electro- 
mechanical contactors and motor- 
starters 



3.0.1 The subject of earthing covers the problems 
relating to the conduction of electricity through earth. 
The terms earth and earthing have been used in this 
Code, irrespective of reliance being placed on the earth 
itself, to denote a low impedance return path of the 
fault current. As a matter of fact, the earth now rarely 
serves as a part of the return circuit but is being used 
mainly for fixing the voltage of system neutrals. The 
earth connection improves service continuity and avoids 
damage to equipment and danger to human lives. 

3.0.2 The object of an earthing system is to provide as 
nearly as possible a surface under and around a station 
which shall be at a uniform potential and as nearly 
zero or absolute earth potential as possible. The purpose 
of this is to ensure that in general all parts of apparatus, 
other than live parts, shall be at earth potential, as well 
as to ensure that operators and attendants shall be at 
earth potential at all times. Also by providing such an 
earth surface of uniform potential under and 
surrounding the station, as nearly as possible, there 
can exist no difference of potential in a short distance 
big enough to shock or injure an attendant when short- 
circuits or other abnormal occurrence take place. 

3.0.3 Earthing associated with current-carrying 
conductor is normally essential to the security of the 
system and is generally known as system earthing, 
while earthing of non-current carrying metal work and 
conductor is essential to the safety of human life, of 
animals and of property and is generally known as 
equipment earthing. 

3.0.4 Earthing shall generally be carried out in 
accordance with the requirements of Indian Electricity 
Rules, 1956 as amended from time to time, and the 
relevant regulations of the electricity supply authority 
concerned. The following clauses of The Indian 
Electricity Rules, 1956 are particularly applicable: 

32, 51, 61, 62, 67, 69, 88 (2) and 90. 

3.0.5 Al medium voltage equipment shall be earthed 
by two separate and distinct connections with earth 
through an earth electrode. In the case of high and extra 
high voltages the neutral points shall be earthed by 
not less than two separate and distinct connections with 
earth each having its own electrode at the generating 
station or sub- station and may be earthed at any other 
point provided no interference is caused by such 
earthing. If necessary, the neutral may be earthed 
through a suitable impedance. 



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3.0.5.1 In cases where direct earthing may prove 
harmful rather than provide safety (for example, high 
frequency and mains frequency coreless induction 
furnaces), relaxation may be obtained from the 
competent authority. 

3.0.6 Earth electrodes shall be provided at generating 
stations, substations and consumer premises in 
accordance with the requirements. 

3.0.7 All far as possible all earth terminals shall be 
visible. 

3.0.8 All connections shall be carefully made; if they 
are poorly made or inadequate for the purpose for 
which they are intended, loss of life or serious personal 
injury may result. 

3.0.9 Each earth system shall be so devised that the 
testing of individual earth electrode is possible. It is 
recommended that the value of any earth system 
resistance shall not be more than 5.0, unless otherwise 
specified. 

3.0.10 It is recommended that a drawing showing the 
main earth connection and earth electrodes be prepared 
for each installation. 

3.0.11 No addition to the current-carrying system either 
temporary or permanent, shall be made, which will 
increase the maximum available earth fault current or 
its duration until it has been ascertained that the existing 
arrangement of earth electrodes, earth busbar, etc, are 
capable of carrying the new value of earth fault current 
which may be obtained by this addition. 

3.0.12 No cut-out, link or switch other than a linked 
switch arranged to operate simultaneously on the 
earthed or earthed neutral conductor and the live 
conductors shall be inserted on any supply system. This 
however, does not include the case of a switch for use 
in controlling a generator or a transformer or a link for 
test purposes. 

3.0.13 All materials, fittings, etc, used in earthing shall 
conform to Indian Standards wherever these exist. In 
the case of materials for which Indian Standard 
specifications do not exist, the materials shall be 
approved by the competent authority. 

3.1 Design Considerations 

3.1.1 System Earthing 

3.1.1.1 The regulations that every medium, high and 
extra high voltage equipment shall be earthed by not 
less than two separate and distinct connections with 
earth is designed primarily to preserve the security of 
the system by ensuring that the voltage on each live 
conductor is restricted to such a value with respect to 
the potential of the general mass of the earth as is 



consistent with the levels of insulation applied. Distinct 
connection with the earth shall be provided for 
lightning protection system for buildings or other 
installations. Distinct earthing system shall be provided 
for centralized electronic system of any building. 

3.1.1.2 The earth system resistance should be such that 
when any fault occurs against which earthing is 
designed to give protection, the protective gear will 
operate to make the faulty portions of plant harmless. 
In most cases such operation involves isolation of the 
faulty main or plant by circuit-breaker or fuses. In the 
cases of underground system there may be no difficulty, 
but in the case of overhead line system protected only 
by fuses there may be difficulty in so arranging the 
value of the earth resistance that a conductor falling 
and making good contact with earth shall cause the 
fuses in the supply to operate. 

NOTE — Earthing may not give protection against faults which 
are not essentially earth faults. For example, if a phase 
conductor of an overhead spur line breaks, and the part remote 
from the supply falls to the ground, it is unlikely that any 
protective gear relying on earthing will operate since the major 
fault is the open-circuit against which earthing gives no 
protection. 

3.1.2 Equipment Earthing 

The object of equipment earthing is to ensure effective 
operation of the protective gear in the event of leakage 
through such metal work, the potential of which with 
respect to neighbouring objects may attain a value 
which would cause danger to life or risk or fire. 

3.1.3 Soil Resistivity 

3.1.3.1 The resistance to earth of an electrode of given 
dimensions is dependent on the electrical resistivity of 
the soil in which it is installed. It follows, therefore, 
that an overriding consideration in deciding which of 
the alternative method of protection is to be adopted 
for a particular system or location is the soil resistivity 
in the area concerned. 

3.1.3.2 The type of soil largely determines its resistivity 
and representative values for soils generally found in 
India are given at Annex B. Earth conductivity is, 
however, essentially electrolytic in nature and is 
affected therefore by moisture content of the soil and 
its chemical composition and concentration of salts 
dissolved in the contained water. Grain size and 
distribution and closeness of packing are also 
contributory factors since they control the manner in 
which the moisture is held in soil. Many of these factors 
vary locally and some seasonally and, therefore, the 
values given in Annex B should be taken only as a 
general guide. Local values should be verified by actual 
measurement and this is especially important where 
the soil is stratified, as owing to the disposition of earth 
current, the effective resistivity depends not only on 



PART 1 GENERAL AND COMMON ASPECTS 



137 



SP 30: 2011 



the surface layers but also on the underlying geological 
formation. 

3.1.33 The soil temperature also has some effect on 
soil resistivity but is important only near and below 
freezing point, necessitating the installation of earth 
electrode at depths to which frost will not penetrate. 

3.1.3.4 While the fundamental nature and properties 
of a soil in a given area cannot be changed, use can be 
made of purely local conditions in choosing suitable 
electrode sites and of methods of preparing the site 
selected, to secure optimum resistivity. Reference is 
drawn to IS 3043. 

3.1.4 Potential Gradients 

It is necessary to ensure, especially in case of large 
electrical installations, that a person walking on the 
ground or touching an earthed objects, in or around the 
premises shall not have large dangerous potential 
differences impressed across his body in case of a fault 
within or outside the premises. Such danger may arise 
if steep potential gradients exist within the premises or 
between boundary of the premises and an accessible 
point outside. For this the step potential and touch 
potential should be investigated and kept within safe 
limits. Within an earthing grid, the step and touch 
potentials may be lowered to any value by reducing 
the mesh interval of the grid. The situation is more 
difficult in the zone immediately outside the periphery 
where the problems may exist even for the theoretical 



case of a single plate covering the sub- station area. This 
problem may be serious in small stations where the grid 
may cover only a limited area. Attempts should be made 
to design a substation so as to eliminate the possibility 
of touch contact beyond the earth-system periphery, 
when the limitations on step potential become less 
exacting. While assessing the touch potential, the 
method of earthing of the object touched, for example, 
whether it is earthed directly below or remotely should 
be kept in view in order to consider the possibility of 
occurrence of large potential differences. 

Special attention should be paid to the points near the 
operating handles of apparatus and, if necessary, 
potential equalizer grillages of closer mesh securely 
bonded to the structure and the operating handle should 
be buried below the surface where the operator may 
stand when operating the switch. 

3.1.5 At consumer's premises where the apparatus is 
protected by fuses, the total earth circuit impedance 
shall not be more than that obtained by graphs given 
in Fig. 1. 

4 EARTH ELECTRODES 

4.1 Material 

4.1.1 Although electrode material does not affect initial 
earth resistance, care should be taken to select a 
material which is resistant to corrosion in the type of 
soil in which it will be used. 




4 6 8 10 12 14 

FUSE RATING IN AMPERES 



Fig. 1 Recommended Earth Circuit Impedance of Resistance for Different Values of Fuse Rating 
138 NATIONAL ELECTRICAL CODE 



SP 30: 2011 



4.1.2 Under ordinary conditions of soil, use of copper, 
iron or mild steel electrodes is recommended. 

4.1.3 In cases where soil conditions point to excessive 
corrosion of the electrode and the connections, it is 
recommended to use either copper electrode or copper 
clad electrode or zinc coated (galvanized) iron 
electrodes. 

4.1.4 In direct current system, however, due to 
electrolytic action which causes serious corrosion, it 
is recommended to use only copper electrodes. 

4.1.5 The electrode shall be kept free from paint, 
enamel and grease. 

4.1.6 It is recommended to use similar material for earth 
electrodes and earth conductors or otherwise 
precautions should be taken to avoid corrosion. 

4.2 Current Loading 

4.2.1 An earth electrode should be designed to have a 
loading capacity adequate for the system in which it 
forms a part, that is, it should be capable of dissipating 
without failure, energy in the earth path at the point at 
which it is installed under any condition of operation 
of the system. Failure is fundamentally due to excessive 
rise of temperature at the surface of the electrode and 
is thus a function of current density and duration as 
well as electrical and thermal properties of soil. 

4.2.2 Two conditions of operation occur in system 
operation, namely; 

a) Long duration overloading as with normal 
system operation, and 

b) Short time overloading as under fault 
conditions in directly earthed system. 

4.3 Voltage Gradient 

4.3.1 Under fault conditions the earth electrode is raised 
to a potential with respect to the general mass of the 
earth. This results in the existence of voltages in the 
soil around the electrode which may be injurious to 
telephone and pilot cables whose cores are substantially 
at earth potential owing to the voltage to which the 
sheaths of such cables are raised. The voltage gradient 
at the surface of the earth may also constitute danger 
to life. 

4.3.2 Earth electrodes should not be installed in 
proximity to a metal fence to avoid the possibility of 
the fence becoming live, and thus dangerous at points 
remote from the substation, or alternatively giving rise 
to danger within the resistance area of the electrode 
which can be reduced only by introducing a good 
connection with the general mass of the earth. If the 
metal fence is unavoidable, it should be earthed. 



4.4 Types of Earth Electrodes 

The following types of earth electrodes are considered 
standard: 

a) Rod and pipe electrodes, 

b) Strip or conductor electrodes, 

c) Plates electrodes, and 

d) Cable sheaths. 

For details regarding their design, reference shall be 
made to IS 3043. 

4.5 Design Data on Earth Electrodes 

4.5.1 The design data on the various types of earth 
electrodes is given in Table 1. 

4.5.2 Effect of Shape on Electrode Resistance 

The resistance of any electrode buried in the earth is in 
fact related to the capacitance of that electrode and its 
image in free space. The relationship is given by: 



#- 



100 p 

AtiC 



where 

R - resistance in an infinite medium; 

p = resistivity of the medium (soil); in ohm- 
metre; and 

C = capacitance of the electrode and its image 
in free space. 

In practical case, the capacitance is divided into two 
by the plane of earth's surface so that, 



R 



100 p 



a) For rod or pipe electrodes, the formula is 

100p log e 2/ohms 

~ AkC d 

where 

/ = length of rod or pipe, in cm; and 
d - diameter of rod or pipe, in cm. 

b) For strip or round conductor electrodes, 



R 



100 p log e 4/ ohms 



AnC 



d 



where 



= length of the strip, in cm; and 



PART 1 GENERAL AND COMMON ASPECTS 



139 



SP 30 : 2011 



/ = width (strip) or twice the diameter 
(conductors), in cm. 

c) For plate electrodes, 



p I /r ohms 
~4VA 



where 

A = area of both sides of plate, in m 2 . 

4.5.3 Effect of Depth of Burial 

To reduce the depth of burial without increasing the 
resistance, a number of rods or pipes shall be connected 
together in parallel (see Fig. 4). The resistance in this 
case is practically proportional to the reciprocal of the 
number of electrodes used so long as each is situated 
outside the resistance area of the other. The distance 
between two electrodes in such a case shall preferably 
be not less than twice the length of the electrode. 

5 EARTH BUS AND EARTH WIRES 

5.0 General 

5.0.1 The minimum allowable size of earth wire is 
determined principally by mechanical consideration for 
they are more liable to mechanical injury and should 
therefore be strong enough to resist any strain that is 
likely to be put upon them. 



5.0.2 All earth wires and earth continuity conductors 
shall be of copper, galvanized iron, or steel or 
aluminium. 

NOTE — Bare aluminium shall not be used underground. 

5.0.3 They shall be either stranded or solid bars or flat 
rectangular strips and may be bare provided due care 
is taken to avoid corrosion and mechanical damage to 
it. Where required, they shall be run inside metallic 
conduits. 

5.0.4 Interconnections of earth- continuity conductors 
and main and branch earth wires shall be made in such 
a way that reliable and good electrical connections are 
permanently ensured. 

NOTE — Welded, bolted and clamped joints are permissible. 
For stranded conductors, sleeve connectors (for example, 
indented, riveted or bolted connectors) are permissible. Bolted 
connectors and their screws shall be protected against any 
possible corrosion. 

5.0.5 The path of the earth wire shall, as far as possible, 
be out of reach of any person. 

5.0.6 If the metal sheath and armour have been used 
as an earth continuity conductor the armour shall be 
bonded to the metal sheath and the connection between 
the earth wire and earthing electrode shall be made to 
the metal sheath. 

5.0.7 If a clamp has been used to provide connection 



Table 1 Design Data on Earth Electrodes 
(Clause 4.5.1 ) 

All dimensions in millimetres. 



SI No. 


Measurement 






Type of Electrodes 










Rod 


Pipe 


Strip 


Round Conductor 




Plate 








(see Note 1) 










(see Note 2) 


(1) 


(2) 


(3) 


(4) 


(5) 




(6) 




(7) 


i) 


Diameter 
(not less than) 


16 mm" 
12.5 mm 2) 


38 mm 1 ' 
100mm 2) 












ii) 


Length of 
conductor/rod 


3 500 mm 


3 500 mm 


500 mm 




15 000 mm 




1 500 mm 


iii) 


Depth upto 
which buried 


3 750 mm 


3 550 mm 










3 200 mm 


iv) 


Size 






25mmx 1.60 mm 2) 
25 mm x 4 mm 11 




3.0mm 22) 
6mm 21) 


1200 
600 


immx 1200 mm 3) 
mm x 600 mm 1 ' 


v) 


Thickness 




3.15 mm 1 ' 










6.30 mm 2) 

3.5 mm 1 ' 


1} Steel or 


galvanized iron. 
















2) Copper. 


















3) Cast iron. 

















NOTES 

1 A typical illustration of pipe earth electrode is given in Fig. 2. 

2 A typical illustration of plate electrode is given in Fig. 3. If two or more plates are used in parallel, they shall be separated by not less 
than 3.0 m. 

3 Adequate quantity of water to be poured into sump every few days to keep the soil surrounding the earth pipe permanently moist. 



140 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



J15. 



TO GROUNDING 
CONDUCTOR 



400 



Mg|~— ^P* 



C 1 COVER HINGED 
TO C I FRAME 










NOTES 

1 All dimensions in millimetres. 

2 After laying the earth from the earth bus to the electrode through the PVC conduits at the pit entry conduits should be sealed with 
bitumin compound. 



Fig. 2 A Typical Illustration of Pipe Earth Electrode 



FART 1 GENERAL AND COMMON ASPECTS 



141 



^ 

M 



2 
> 

H 

8 

r 

n 
o 

H 

2 

r 
r> 
o 

© 



CAST IRON OR 
C I COVER 



ITO^W^ 




WELDED 



50X12 

G I STRIP WXl 



1000X500X600 

THSHBblK ft 

CHAMBER 



CEMENT 

CONCRETE . 



.0 5OGIPIPE 





1200x1200X12 Ci PLATE 

CHARCOAL AND SALT 




50 x 1-2 G I STRIP 







o 



012X60 LONG G I 
&6L.TS & NUTS, CHECK NUT 
& WASHER (AFTER FIXING, THE 
OUTSIDE SURFACE SHOULD 
BE COVERED WITH BITUMIN) 



DETAIL A 



800 



I f t t fc 




G I STRIP 



1200X1200X12 
Ci PLATE 



DETAIL B 



12X6OLQNGGI 
BOLTS & NUTS t CHECK NUT 
& WASHER (AFTER FIXING, THE 
OUTSIDE SURFACE SHOULD 
BE COVERED WITH BITUMIN) 



10 G I BOLT LENGTH 
50 (AFTER FIXING, THE 
OUTSIDE SURFACE SHOULD 
BE COVERED WITH BmifUtlN) 




50 x 12 G I STRIP 



DETAIL C 



All dimensions in millimetres. 

3A Earthing with GI Plate 
Fig. 3 A Typical Illustration of Plate Earth Electrode 



Continued 



H 

o 
m 

o 
S 
S 
o 

ft 

n 

H 
as 



CAST IRON OR 
CI COVER 



35 X 6 COPPER STRIP 



12X40 LONG BRASS 




BOLTS & NUTS, CHECK NUT 
a WASHER (AFTER FIXING, THE 
OUTSIDE SURFACE SHOULD 
BE COVERED WITH BiTUMIN) 



600X600X3 



DETAIL B 



12X40 LO NG BRASS 
BOLTS & NUTS, CHECK NUT 
& WASHER (AFTER FIXING, THE 
OUTSIDE SURFACE SHOULD 
BE COVERED WITH BITUMIN) 



COPPER PLATE 



10 BRASS BOLT LENGTH 
30 (AFTER FIXING, THE 
OUTSIDE SURFACE SHOULD 
BE COVERED WTTH BITUMIN) 




25 X 4 COPPER STRIP 
FOR CLAMP 



DETAIL C 






All dimensions in millimetres. 

3B Earthing with Copper Plate 
Fig. 3 A Typical Illustration of Plate Earth Electrode 



m 

© 
© 



SP 30 : 2011 




2 4 6 8 10 12 14 16 

INDIVIDUAL RESISTANCE IN OHMS 



18 



Fig. 4 Resistance of Electrode at Various Depths and Soil Resistances 



between the earth wire and the metal sheath and armour, 
it shall be so designed and installed as to provide reliable 
connection without damage to the cable. 

5.0.8 The neutral conductor shall not be used as earth 
wire. 

5.0.9 The minimum sizes of earth-continuity 
conductors and earth wires shall be as given in the 
relevant part of the Code. 

6 MEASUREMENT OF EARTH ELECTRODE 
RESISTANCE 

6.1 Fall of Potential Method 

In this method two auxiliary earth electrodes, 
besides the test electrode, are placed at suitable 
distances from the test electrode (see Fig. 5). A 
measured current is passed between the electrode 
'A' to be tested and an auxiliary current electrode 
'C and the potential difference between the 
electrode 'A' and the auxiliary potential electrode 
'5' is measured. The resistance of the test electrode 
'A' is then given by: 



R. 



V_ 

I 



where 

R = resistance of the test electrode, in ohms; 
V = reading of the voltmeter, in V; and 
/ = reading of the ammeter, in amperes. 

144 



<*> 



^AMMETER 



CURRENT ~ ~V ^ 

SOURCE Q / y VVOLTME TER 






Y777?. 



777777777, 



777777777? 



* » tro 



>/7777Z 



TEST 

ELECTRODE 



POTENTIAL 
ELECTRODE 



CURRENT 
ELECTRODE 



Fig. 5 Method of Measurement of Earth 
Electrode Resistance 

6.1.1 If the test is made at power frequency, that is, 
50 Hz, the resistance of the voltmeter should be high 
compared to that of the auxiliary potential electrode 
'IT and in no case should be less than 20 000 Q. 

NOTE — In most cases there will be stray currents flowing in 
the soil and unless some steps are taken to eliminate their effect, 
they may produce serious errors in the measured value. If the 
testing current is of the same frequency as the stray current, 
this elimination becomes very difficult and it is better to use 
an earth tester incorporating a hand-driven generator. These 
earth testers usually generate direct current and have rotary 
current-reverser and synchronous rectifier mounted on the 
generator shaft so that alternating current is supplied to the 
test circuit and the resulting potentials are rectified for 
measurement by a direct-reading moving-coil ohm-meter. The 
presence of stray currents in the soil is indicated by a wandering 
of the instrument pointer, but an increase or decrease of 
generator handle speed will cause this to disappear. 

6.1.2 The source of current shall be isolated from the 
supply by a double by a double wound transformer. 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



6.1.3 At the time of test, where possible, the test 
electrode shall be separated from the earthing system. 

6.1.4 The auxiliary electrodes usually consist of 
12.5 mm diameter mild steel rod driven up to 1 m into 
the ground. 

6.1.5 All the test electrodes and the current electrodes 
shall be so placed that they are independent of the 
resistance area of each other. If the test electrode is in 
the form of rod, pipe or plate, the auxiliary current 
electrode ' C shall be placed at least 30 m away from 
it and the auxiliary potential electrode '/?' shall be 
placed midway between them. 

6.1.6 Unless three consecutive readings of test electrode 
resistance with different spacings of electrodes agree, 
the test shall be repeated by increasing the distance 
between electrodes 'A' and 'C up to 50 m and each 
time placing the electrode *#' midway between them. 

6.2 Alternative Method 

6.2.1 The method described in 6.1 may not give 
satisfactory results if the test electrode is of very low 
impedance (1 ohm or less). This applies particularly 
while measuring the combined resistance of large 
installations. In these cases, the following method may 
be adopted. 

6.2.1.1 Two suitable directions, at least 90° apart, are 
first selected. The potential lead is laid in one direction 
and an electrode is placed 250 to 300 m from the fence. 
The current lead is taken in the other direction and the 
current electrode located at the same distance as the 
potential electrode. A reading is taken under this 
condition. The current electrode is then moved out in 
30 m steps until the same reading is obtained for three 
consecutive locations. The current electrode is then left 
in the last foregoing position and the potential electrode 
is moved out in 30 m steps until three consecutive 
readings are obtained without a change in value. The 
last readings then correspond to the true value of earth 
resistance. 

7 EARTHING OF INSTALLATIONS IN 
BUILDINGS 

7.1 The earthing arrangements of the consumer's 
installation shall be such that on occurrence of a fault 
of negligible impedance from a phase or non-earthed 
conductor to adjacent exposed metal, a current 
corresponding to not less than three-and-a-half times 
the rating of the fuse or one-and-a-half times the setting 
of the overload earth leakage circuit- breaker will flow 
except where residual current operated devices or 
voltage operated earth leakage circuit-breakers are used 
and make the faulty circuit dead. Where fuses are used 
to disconnect the faulty section of an installation in 



the event of an earth fault, the total permissible 
impedance of the earth fault path may be computed 
from the following formula (for a normal three-phase 
system with earthed neutral). 



Z = - 



Phase-to-earth voltage of system 
Minimum fusing current off ues x Factor of safety 



where 

Z = permissible impedance, in ohm. 

NOTE — The factor of safety in calculating the permissible 
impedance should be left to the discretion of the designer. 

7.1.1 The factor of safety in the above formula ensures 
that in most cases the fuse will blow in a time which is 
sufficiently short to avoid danger and allowing for a 
number of circumstances, such as the grading of fuse 
rating, increase of resistance due to drying out of the 
earth electrodes in dry weather, inevitable extensions 
to installations involving increase in length of the circuit 
conductors and the earth-continuity conductors, etc. 

7.1.2 It will be observed that this requirement 
determines the overall impedance and does not contain 
a specific reference to any part of the circuit such as 
the conduit or other earth-continuity conductor together 
with the earthing lead. In fact, in large installations the 
overall impedance permissible may be less than 1 ohm, 
so that considerably less than this might be allowable 
for the earth-continuity system. 

7.2 It is desirable when planning an installation to 
consult the supply authority or an electrical contractor 
having knowledge of local conditions, in order to 
ascertain which of the two, namely, the use of fuses of 
overload circuit-breakers, for protection against earth- 
leakage currents is likely to prove satisfactory. 

7.3 It is recommended that the maximum sustained 
voltage developed under fault conditions between 
exposed metal required to be earthed and the 
consumer's earth terminal shall not exceed 32 V rms. 

7.4 Only pipe, rod or plate earth electrodes are 
recommended and they shall satisfy the requirements 
of 4.5. 

7.5 Earth-Continuity Conductors 

7.5.1 Connection to earth of those parts of an 
installation which require to be earthed shall be made 
by means of an earth-continuity conductor which may 
be a separate earth conductor, the metal sheath of the 
cables or the earth continuity conductor contained in a 
cable, flexible cable or flexible cord. 

7.5.2 Earth-Continuity Conductors and Earth Wires 
not Contained in the Cables 

The size of the earth-continuity conductors should be 



PART 1 GENERAL AND COMMON ASPECTS 



145 



SP 30: 2011 



correlated with the size of the current carrying 
conductors, that is, the sizes of earth-continuity 
conductors should not be less than half of the largest 
current carrying conductors, provided the minimum 
size of earth-continuity conductors is not less than 
1.5 mm 2 for copper and 2.5 mm 2 for aluminium and 
need not be greater than 70 mm 2 for copper and 
120 mm 2 for aluminium. As regards the sizes of 
galvanized iron and steel earth-continuity conductors, 
they may be equal to size of current-carrying 
conductors with which they are used. The size of earth- 
continuity conductors to be used along with aluminium 
current-carrying conductors should be calculated on 
the basis of equivalent size of the copper current- 
carrying conductors. 

7.5.3 Earth-Continuity Conductors and Earth Wires 
Contained in the Cables 

For flexible cables, the size of the earth-continuity 
conductors should be equal to the size of the current- 
carrying conductors and for metal sheathed, PVC and 
tough rubber sheathed cables the sizes of the earth- 
continuity conductors shall be in accordance with 
relevant Indian Standards. 

7.5.4 Cable Sheaths Used as Earth-Continuity 
Conductors 

Where the metal sheaths of cables are used as earth- 
continuity conductors, every joint in such sheaths shall 
be so made that its current-carrying capacity is not less 
than that of the sheath itself. Where necessary, they 
shall be protected against corrosion. 

Where non-metallic joint boxes are used, means shall 
be provided to maintain the continuity, such as a metal 
strip having a resistance not greater than that of the 
sheath of the largest cable entering the box. 

7.5.5 Metal Conduit Pipe Used as on Earth-Continuity 
Conductor 

Metal conduit pipe should generally not be used as an 
earth-continuity conductor but where used as very high 
standard of workmanship in installation is essential. 
Joints shall be so made that their current-carrying 
capacity is not less than that of the conduit itself. 
Slackness in joints may result in deterioration and even 
complete loss of continuity. Plain slip or pin-grip 
sockets are insufficient to ensure satisfactory electrical 
continuity of joints. In the case of screwed conduit, 
lock nuts should also be used. 

7.5.6 Pipes and Structural Steel Work 

Pipes, such as water pipe, gas pipe, or members of 
structural steel work shall not be used as earth- 
continuity conductor. 



8 MEASUREMENT OF EARTH LOOP 
IMPEDANCE 

8.1 The current which will flow under earth fault 
conditions and will thus be available to operate the 
overload protection depends upon the impedance of 
the earth return loop. This includes the line conductor, 
fault, earth-continuity conductor and earthing-lead, 
earth electrodes at consumer's premises and substations 
and any parallel metallic return to the transformer 
neutral as well as the transformer winding. To test the 
overall earthing for any installation depending for 
protection on the operation of overcurrent devices, for 
example, fuses, it is necessary to measure the 
impedance of this loop under practical fault conditions. 
After the supply has been connected this shall be done 
by the use of an earth loop impedance tester as shown 
in Fig. 6. The neutral is used in place of the phase 
conductor for the purpose of the test. The open-circuit 
voltage of the loop tester should not exceed 32 V. 

9 TYPES OF SYSTEM EARTHING 

9.1 Internationally, it has been agreed to classify the 
earthing systems as TN System, TT System and IT 
System. 

9.1.1 TN System 

This type of system has one or more points of the source 
of energy directly earthed, and the exposed and 
extraneous conductive parts of the installation are 
connected by means of protective conductors to the 
earthed point(s) of the source, that is, there is a metallic 
path for earth fault currents to flow from the installation 
to the earthed point(s) of the source. TN systems are 
further sub-divided into TN-C, TN-S and TN-C-S 
systems. 

9.1.2 TT System 

This type of system has one or more points of the source 
of energy directly earthed and the exposed and 
extraneous conductive parts of the installation are 
connected to a local earth electrode or electrodes and 
are electrically independent of the source earth(s). 

9.1.3 IT System 

This type of system has the source either unearthed or 
earthed through a high impedance and the exposed 
conductive parts of the installation are connected to 
electrically independent earth electrodes. 

9.1.4 It is also recognized that, in practice, a system 
may be an admixture of types. For the purpose of this 
Code, earthing systems are designated as follows: 

a) TN-S system (for 240 V single-phase domestic/ 
commercial supply) — Systems where there 
are separate neutral and protective conductors 



146 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



V) VOLTMETER 




A = ammeter 

B = neon indicator 

C = main switch 

D = test switch 

E - consumer's earth electrode 



F = supply fuse 

P = polarity switch 

S - substation earth electrode 

V = voltmeter 



At FF y jacks are provided for insertion of plugs for connection to externa) neutral and/or earth conductors, if desired. 

NOTES 

1 Arrows shows current flow in neutral or earth loop. 

2 Supply system is shown in dotted. 

Fig. 6 Circuit Diagram of Earth Loop Impedance Tester 



throughout the system. A system where the 
metallic path between the installation and the 
source of energy is the sheath and armouring 
of the supply cable (see Fig. 7 A). 

b) Indian TN-S System (for 415 V three-phase 
domestic commercial supply) — An 
independent earth electrode within the 
consumer's premises is provided (see Fig. 7B). 

c) Indian TN-C System — The neutral and 
protective functions are combined in a single 
conductor throughout the system (for example 
earthed concentric wiring (see Fig. 7C). 



SOURCE OF ENERGY 

rz> 



SOURCE 
EARTH 



EQUIPMENT IN 
INSTALLATION 



i 



-12 
-13 



-PE 






' * 

w-" 



EXPOSED 

CONOUCTIVE 

PART 
CONSUMER 
INSTALLATION 



NOTE — The protective conductor (PE) is the metallic covering 
(armour or load sheath of the cable supplying the installation 
or a separate conductor). All exposed conductive parts of an 
installation are connected to this protective conductor via main 
earthing terminal of the installation. 

7A TN-S System Separate Neutral and Protective 
Conductors Throughout the System, 230V Simple 
Phase. Domestic/Commercial Supply for 3 ~ TN-S 



d) TN-C-S System — The neutral and protective 
functions are combined in a single conductor 
but only in part of the system (see Fig. 7D). 

e) T-TN-S System (for 6. 6/1 1 kV three-phase bulk 
supply) — The consumers installation, a TN- 
S system receiving power at a captive 
substation through a delta connected 
transformer primary (see Fig. 7E). 

f) 7T System (for 415V three-phase industrial 
supply) — Same as 9.1.2 (see Fig. 7F) 

g) IT System — Same 9.1.3 (see Fig. 7G). 



SOURCE OF ENERGY 



ZZ3 : : < 




























I 

1 


S 1 


> i 


► i 


> « 


■""71 L, | 


1 

1 


M 


► i 


► < 


u 





12 
13 
H 



NOTE — For 415 V Three Phase Domestic/Commercial 
Supply Having 3-Phase and 1-Phase Loads. All exposed 
conductive parts of the installation are connected to protective 
conductor via the main earthing terminal of the installation. 
An independent earth electrode within the consumer's premises 
is also provided. 

7B Indian TN-S System 



Fig. 7 Types of System Earthing — (Continued) 



PART 1 GENERAL AND COMMON ASPECTS 



147 



SP 30 : 2011 



SOURCE OF ENERGY 



SOURCE OF ENERGY 




3 ^CONSUME 



NOTE — All exposed conductive parts are connected to the 
PEN conductor. For 3~ consumer, local earth electrode has to 
be provided in addition. 

7C Indian TN-C System (Neutral and Protective 

Functions Combined in a Single Conductor 

Throughout System) 



COMBINED 
PE tN 



=5— H 


> i " 


> 






^3 




i, 


r 


— 


< 


M 


Is 


-]I 






C 


n 


UAjj 


1 
1 












1 



NOTE — The usual form of a TN-C-S system is as shown, 
where the supply is TN-C and the arrangement in the 
installations in TN-S. This type of distribution is known also 
as Protective Multiple Earthing and the PEN conductor is 
referred to as the combined neutral and earth (CNE) conductor. 
The supply system PEN conductor is earthed at several points 
and an earth electrode may be necessary at or near a consumer' s 
installation. All exposed conductive parts of an installation are 
connected to the PEN conductor via the main earthing terminal 
and the neutral terminal, these terminals being linked together. 
The protective neutral bonding (PNB) is a variant of TN-C-S 
with single point earthing. 

7D TN-C-S System, Neutral and Protective 

Functions Combined in a Single Conductor in a 

Part of the System 

SOURCE OF ENERGY 



tza- 



r 



IAI 



CONSUMER 

INSTALLATION 



« 



Wk 



■JT 



-12 



6 6 6 

3*^> LOAD 



CONSUMER 
INSTALLATION 



^13 



IviLOAD 

— I 



3^L0A0 



- ? 

-2 
-3 



6.6/1 1 kV Three phase bulk supply. 

7E T-TN-S System 

Fig. 7 Types of System Earthing — (Continued) 



SOURCE 
EARTH 



CONSUMER f 
INSTALLATION 



fi= 



L. 



t 



XX 



INSTALLATION 

EARTH 
ELECTRODE 



415 V Three phase industrial supply having 3-phase and 
1 -phase loads. 

NOTE — All exposed conductive parts of the installation are 
connected to an earth electrode which is electrically 
independent of the source earth. Single phase TT system are 
not present in India. 

7F TT System 



SOURCE OF 
ENEROY 



r 



** lJ r ?_i l 



-L2 

-13 



vl 



NOTE — All exposed conductive parts of an installation are 
connected to an earth electrode. 

The source is either connected to earth through a deliberately 
introduced earthing impedance or is isolated from earth. 

7G IT System 
Fig. 7 Types of System Earthing 

10 SELECTION OF DEVICES FOR 
AUTOMATIC DISCONNECTION OF SUPPLY 

10.1 General 

In general, every circuit is provided with a means of 
overcurrent protection. If the earth fault loop 
impedance is low enough to cause these devices to 
operate within the specified times (that is, sufficient 
current can flow to earth under fault conditions), such 
devices may be relied upon to give the requisite 
automatic disconnection of supply. If the earth fault 
loop impedance does not permit the overcurrent 
protective devices to give automatic disconnection of 
the supply under earth fault conditions, the first option 
is to reduce that impedance. It may be permissible for 
this to be achieved by the use of protective multiple 
earthing or by additional earth electrodes. There are 
practical limitations to both approaches. 

In case of impedance/arcing faults, series protective 
devices may be ineffective to clear the faults. An 
alternate approach is to be adopted for the complete 
safety of the operating personnel and equipment from 
the hazards that may result from earth faults. This is to 



148 



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use residual current devices with appropriate settings 
to clear the faults within the permissible time, based 
on the probable contact potential. This method is 
equally applicable where earth loop impedances cannot 
be improved. 

In TT systems, there is an additional option of the use 
of fault voltage operated protective devices; whilst 
these devices will always give protection against shock 
risk, provided they are correctly installed, the presence 
of parallel earths from the bonding will reduce the 
effectiveness of the fire risk protection they offer. These 
are, therefore, more suited for isolated installations that 
do not have interconnections to other installations. It 
should also be remembered that every socket outlet 
circuit that do not have earthing facility in a household 
or similar installation should be protected by a residual 
current device having a rated residual operating current 
not exceeding 30 mA. 

On all other systems where equipment is supplied by 
means of a socket outlet not having earthing facility or 
by means of a flexible cable or cord used outside the 
protective zone created by the main equipotential 
bonding of the installation such equipment should be 
protected by a residual current operated device having 
an operating current of 30 mA or less. 

NOTE — Information on cascading, limitation and 
discrimination is given at Annex C. 

10.2 Use of Over-Current Protective Devices for 
Earth Fault Protection 

Where over-current protective devices are used to give 
automatic disconnection of supply in case of earth fault 
in order to give shock risk protection, the basic 
requirement is that any voltage occurring between 
simultaneously accessible conductive parts during a 
fault should be of such magnitude and duration as not 
to cause danger. The duration will depend on the 
characteristic of the overcurrent device and the earth 
fault current which, in turn, depends on the total earth 
fault loop impedance. The magnitude will depend on 
the impedance of that part of the earth fault loop path 
that lies between the simultaneously accessible parts. 

The basic requirement can be met if, 

a) a contact potential of 65 V is within the 
tolerable limits of human body for 10 s. Hence 
protective relay or device characteristic should 
be such that this 65 V contact potential should 
be eliminated within 10 s and higher voltages 
with shorter times. 

b) a voltage of 250 V can be withstood by a 
human body for about 100 ms, which requires 
instantaneous disconnection of such faults, 
giving rise to potential rise of 250 V or more 
above the ground potential. 



The maximum earth fault loop impedance 
corresponding to specific ratings of fuse or miniature 
circuit-breaker that will meet the criteria can be 
calculated on the basis of a nominal voltage to earth 
(U ) and the time current characteristics of the device 
assuming worst case conditions, that is, the slowest 
operating time accepted by the relevant standards. 
Thus, if these values are not exceeded, compliance with 
this Code covering automatic disconnection in case of 
an earth fault is assured. 

Where it is required to know the maximum earth fault 
loop impedance acceptable in a circuit feeding, a fixed 
appliance or set of appliances and protected by an over 
current device, the minimum current that may be 
necessary to ensure operation of the overcurrent device 
within the permissible time of 10 s for a contact 
potential of 65 V is found from the characteristic curve 
of the device concerned. Application of the Ohm's Law 
then enables the corresponding earth fault loop 
impedance to be calculated. 

For circuits supplying socket outlets, the corresponding 
earth fault loop impedance can be found by a similar 
calculation for earthed equipment. When equipment 
are not earthed and connected to socket outlets without 
earthing facility, disconnection should be ensured for 
30 mA within 10 s and with appropriate decrements in 
time for higher currents. 

This method requires a knowledge of the total earth 
loop impedance alone (rather than individual 
components) and is, therefore, quick and direct in 
application. Its simplicity does exclude some circuit 
arrangements that could give the required protection. 

While calculations give the maximum earth fault loop 
or protective conductor impedance to ensure shock risk 
protection under fault conditions it is also necessary to 
ensure that the circuit protective earth conductor is 
protected against the thermal effects of the fault current. 
The earth fault loop impedance should, therefore, be low 
enough to cause the protective device to operate quickly 
enough to give that protection as well. This consideration 
places a second limit on the maximum earth loop 
impedance permissible and can be checked by 
superimposing on the time current characteristic of the 
overload device, the 'adiabatic' line having the equation: 



k 2 A 2 
I 2 



-or A = 



Iyft 



Details of the maximum permissible earth loop 
impedance for the thermal protection of cables by fuses 
can also be computed. However, the time current 
characteristics of a miniature circuit-breaker are such 
that if the loop impedance is low enough to give 
automatic disconnection within safe disconnecting time 



PART 1 GENERAL AND COMMON ASPECTS 



149 



SP 30 : 2011 



so providing shock risk protection, it will also give 
the necessary thermal protection to the earth conductor 
likely to be used with a breaker of that specific rating. 
Figure 8 shows the relationship between the adiabatic 
line and the characteristic of fuses and miniature circuit- 
breaker. 



FUSE CHARACTERISTICS 




A DIABATIC LINE 



CURRENT I - 



8A Fuses 



MCB CHARACTERISTICS 




CURRENT I - 



8B Miniature Circuit-breaker 

Fig. 8 Relationship Between Adiabatic Lines 
and Characteristics 

In order that the devices will give thermal protection 
to the protective conductor, operation has to be 
restricted to the area to the right of point A where these 
curves cross. Thus, the maximum earth fault loop 
impedance for thermal protection of the cable is that 
corresponding to the minimum earth fault current for 
which the device gives protection. The value of this 
current can be read from the curve and the 
corresponding loop impedance can be calculated from: 

where 

Z s = earth fault loop impedance, 
U = nominal voltage to earth, and 



I t = earth fault current. 

For a given application, the maximum permitted earth 
fault loop impedance would be the lower of the two 
values calculated for shock risk protection or thermal 
restraint respectively. 

It will be noted that the adiabatic line crosses the 
characteristic curve for a miniature circuit-breaker at 
a second point B. This denotes the maximum fault 
current for which a breaker will give thermal protection 
but it will generally be found in practice that this value 
is higher than the prospective short circuit current that 
occurs in the circuit involved and cannot, therefore, be 
realized. 

10.3 Earth Fault Protective Devices 

There are two basic forms of such devices that can be 
used for individual non-earthed/earthed (with limited 
application) equipment as follows: 

10.3.1 Residual Current Operated Devices (RCD) 

An RCD incorporates two component items. A core 
balance transformer assembly with a winding for each 
recognizing the out of balance current that the fault 
produces in the main conductors. This induces a current 
that is used to operate the tripping mechanism of a 
contact system. For operating currents of 0.5 A or more, 
the output from such a transformer assembly can 
operate a conventional trip coil directly. For lower 
values of operating current, it is necessary to interpose 
a delay device, either magnetic or solid state. 

Devices for load currents greater than 100 A usually 
comprise a separate transformer assembly with a circuit- 
breaker or contact relay, mounted together within a 
common enclosure. Devices for load currents below 
100 A usually include the transformer and contact 
system within the same single unit, which is then 
described as a residual current operated circuit- breaker 
(RCB). Such an RCB should be considered a particular 
type of RCB although it is the most usual form. 

A wide choice of operating currents is available (typical 
values are between 10 mA and 20 A ) RCB's are normally 
non-adjustable whilst RCD's are often manufactured so 
that one of several operating currents may be chosen. 
Single phase and multiphase devices with or without 
integral overcurrent facilities are available. 

Where residual current breakers of 30 mA operating 
current or less are being used, there is a choice between 
devices that are entirely electromechanical in operation 
and those that employ a solid state detector. The 
electromechanical types are generally small and compact 
and will operate on the power being fed to the fault alone 
whereas the solid state type which tend to be bulkier to 
require a power supply to ensure operation. Where this 
power supply is derived from the mains, it may be 



150 



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necessary to take added precaution against failures of 
part of that mains supply. Devices suitable for time 
grading are more likely to be of the solid state form as 
are those having higher through fault capacity. 

A test device is incorporated to allow the operation of 
the RCD to be checked. Operation of this device creates 
an out of balance condition within the device. Tripping 
of the RCD by means of the test device establishes the 
following: 

a) The integrity of the electrical and mechanical 
elements of the tripping device; and 

b) That the device is operating at approximately 
the correct order of operating current. 

It should be noted that the test device does not provide 
a means of checking the continuity of the earthing lead 
or the earth continuity conductor, nor does it impose 
any test on the earth electrode or any other part of the 
earthing circuit. 

Although an RCD will operate on currents equal to or 
exceeding its operating current, it should be noted that 
it will only restrict the time for which a fault current 
flows. It cannot restrict the magnitude of the fault percent 
current which depends solely on the circuit conditions. 

10.3.2 Fault Voltage Operated Earth Leakage Circuit 
Breakers (ELCB) 

A voltage operated earth leakage circuit-breaker 
comprises a contact switching system together with a 
voltage sensitive trip coil. On installations, this coil is 
connected between the metal-work to be protected and 
as good a connection with earth as can be obtained. 
Any voltage rise above earth on that metal-work 
exceeding the setting of the coil will cause the breaker 
to trip so giving indirect shock risk protection. 

Tripping coils are designed so that a fault voltage 
operated device will operate on a 40 V rise when the 
earth electrode resistance is 500 W or 24 V on a 200 W 
electrode. Single and multiphase units, with or without 
overcurrent facilities, are available for load currents 
up to 100 A. 

A test device is provided on a voltage operated unit to 
enable the operation of the circuit breaker to be 
checked, operation of the device applies a voltage to 
the trip coil so simulating a fault. Tripping of the circuit 
breaker by means of the test device shows the integrity 
of the electrical mechanical elements that the unit is 
operating with the correct order of operating voltage 
and, in addition, proves the conductor from the circuit 
breaker to the earth electrode. It can not prove other 
features of the installation. 

Whilst the voltage operated ( ELCB ) will operate when 
subjected to a fault voltage of 20 V or more, it should 



be noted that it cannot restrict the voltage in magnitude 
only in duration. 

10.3.3 Current Operated Earth Leakage Circuit -Breakers 

For industrial applications, earth leakage circuit- 
breakers operating on milliampere residual currents or 
working on fault voltage principle are of little use, since 
milliamperes of earth leakage current for an extensive 
industrial system is a normal operating situation. 
Tripping based on these currents will result in nuisance 
for the normal operation. Milliamperes of current in a 
system, where exposed conductive parts of equipments 
are effectively earthed and fault loop impedance is 
within reasonable values, will give rise only to a ground 
potential/contact potential rise of a few millivolts. This 
will in no way contribute to shock or fire hazard. Here 
objectionable fault currents will be a few or a few tenths 
of amperes. In such cases, residual current operated 
devices sensitive to these currents must be made use 
of for earth fault current and stable operation of the 
plant without nuisance tripping. This is achieved either 
by separate relays or in-built releases initiating trip 
signals to the circuit-breakers 

10.4 Selection of Earth Fault Protective Devices 

In general, residual current operated devices are 
preferred and may be divided into two groups 
according to their final current operating 
characteristics. 

10.4.1 RCDs having Minimum Operating Currents 
Greater than 30 mA 

These devices are intended to give indirect shock risk 
protection to persons in contact with earthed metal. 

10*4.2 RCDs having Minimum Operating Current of 
30 mA and Below 

These devices are generally referred to as having 'high 
sensitivity' and can give direct shock risk protection 
to persons who may come in contact with live 
conductors and earth provided that the RCD operating 
times are better than those given in IS 8437 (Part 1) 
and IS 8437 (Part 2). It should be noted that such RCDs 
can only be used to supplement an earth conductor 
and not replace one. 

In addition to giving protection against indirect contact 
or direct contact RCDs may also give fire risk 
protection, the degree of protection being related to 
the sensitivity of the device. 

An RCD should be chosen having the lowest suitable 
operating current. The lower the operating current the 
greater the degree of protection given, it can also 
introduce possibilities of nuisance tripping and may 
become unnecessarily expensive. The minimum 
operating current will be above any standing leakage 



PART 1 GENERAL AND COMMON ASPECTS 



151 



SP 30: 2011 



that may be unavoidable on the system. A further 
consideration arises if it is intended to have several 
devices in series. It is not always possible to introduce 
time grading to give discrimination whereas a limited 
amount of current discrimination can be obtained by 
grading the sensitivities along the distribution chain. 

The maximum permitted operating current depends on 
the earth fault loop impedance. The product of the net 
residual operating current loop impedance should not 
exceed 65 V. 

It is often acceptable on commercial grounds to have 
several final circuits protected by the same residual 
current devices. This, however, does result in several 
circuits being affected if a fault occurs on one of the 
circuits so protected and the financial advantages have 
to be weighed against the effects of loosing more than 
one circuit. 

It should also be noted that different types of RCD in 
different circuits may react differently to the presence 
of a neutral to earth fault on the load side. Such an 
earth connection together with the earthing of the 
supply at the neutral point will constitute a shunt across 
the neutral winding on the RCD transformer. 
Consequently, a portion of the neutral load current will 
be shunted away from the transformer and it may result 
in the device tripping. On the other hand, such a shunt 
may reduce the sensitivity of the device and prevent 
its tripping even under line to earth fault conditions. 
In general, therefore, care should be taken to avoid a 
neutral to earth fault where RCDs are in use, although 



there are some designs being developed that will detect 
and operate under such conditions. On installations 
with several RCDs, care should be taken to ensure that 
neutral currents are returned via the same device that 
carries the corresponding phase current and no other. 
Failure to observe this point could result in devices 
tripping even in the absence of a fault on the circuit 
they are protecting. 

When using fault voltage operated ELCBs, the 
metal-work to be protected should be isolated from 
earth so that any fault current passes through the 
tripping coil gives both shock and fire risk protection. 
However, this isolation is not always practicable and 
the presence of a second parallel path to earth will 
reduce the amount of fire risk protection offered. 
Because the coil is voltage sensitive, the presence of 
such a parallel path will not reduce the shock risk 
protection offered provided that this second path goes 
to earth well clear of the point at which the earth 
leakage circuit-breaker trip coil is earthed. It is required 
that the earthing conductor is insulated to avoid contact 
with other protective conductors or any exposed 
conductive parts or extraneous conductive parts so as 
to prevent the voltage sensitivity element from being 
shunted, also the metal- work being protected should 
be isolated from that associated with other circuits in 
order to prevent imported faults. 

NOTE — For hybrid Indian TN-S system it is recommended 
that RCD protection is provided in addition to the overcurrent 
protection provided for earth fault protection. This will ensure 
required protection in case of any break in continuity of the 
protective earth conductor. 



ANNEX A 
(Clause 1) 

ADDITIONAL RULES FOR EARTHINGS 



A-l ADDITIONAL RULES APPLYING TO THE 
DIRECT EARTHING SYSTEM 

Where a driven or buried electrode is used, the earth 
resistance shall be as low as possible. 

NOTE — The value of earth resistance is under consideration. 

A-2 ADDITIONAL RULES APPLYING TO THE 
MULTIPLE EARTH NEUTRAL SYSTEM 

This system shall be used only where the neutral and 
earth is low enough to preclude the possibility of a 
dangerous rise of potential in the neutral. 

A-3 ADDITIONAL RULES APPLYING TO THE 
EARTH LEAKAGE CIRCUIT-BREAKER SYSTEM 

A-3.1 Installation of the Earth Leakage Circuit- 
Breaker System (see Fig. 9) 



All parts required to be earthed shall be connected to 
an earth electrode through the coil of an earth leakage 
circuit-breaker which controls the supply to all those 
parts of the installation which are to be protected; and 
to a separate earth electrode. 

A-3 2 Selective Protection 

If selective operation of earth leakage circuit-breaker 
is required, the circuit-breaker, electrodes and earthing 
conductors shall be installed in one of the following 
ways: 

a) Arrangement Giving Complete Selectivity — 
All metal frames, conduits, earthing 
conductors, etc, which are to be protected as 
a unit shall be electrically separated from all 
other such parts and from any other earthed 
metal. Each part to be protected as a unit shall 



152 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



E.LC.B. 



PLUG - SOCKET 
OUT LETS 




.EQUIPMENT 
Fig. 9 Connection of Earth Leakage Circuit-Breaker Simple Installation 



INSULATED 
CONDUCTOR 




MAY BE BARE 



CONDUITS SHALL 
NOT TOUCH 
<mirt. RESIS- 
TANCE 5000 
DHMS) 



10A Complete Separation of the Exposed Metal of 10B By Use of a Double-Insulated Wiring System, 

One Installation from that of Other Installation Where There are no Conduits to be Earthed 



Fig. 10 Connection of Earth Leakage Circuit-Breaker for Complete Selectivity 
PART 1 GENERAL AND COMMON ASPECTS 153 



SP 30:' 2011 



be connected to an earth electrode through 
the coil of an earth leakage circuit-breaker. 
(see Fig. 10) 

All the separately protected portions of the 
installations may be connected to one 
electrode to the earth leakage circuit-breaker. 

b) Arrangement Giving Partial Selectivity 
(Complete Selectivity with Respect to Faults 
in Apparatus, but no Selectivity with Respect 
to Faults in Wiring in Conduit) (see Fig. 9) — 
All the conduits and associated fittings shall 
be bonded together and connected to an earth 
electrode, all shall also be connected to 
another earth electrode through an earth 
leakage circuit-breaker which controls all the 



active conductors supplying the whole or 
portions of the installations concerned. Each 
part to be protected as a unit shall be 
connected to an earth electrode through the 
coil of a separate earth leakage circuit-breaker 
which controls all the active conductors 
supplying that portion of the installation only. 
All these portions may be connected to one 
electrode, but this electrode shall be separated 
from the electrode to which the conduits are 
connected. 

NOTES 

1 A double-insulated wiring system is used, for example, 
tough rubber-sheathed cables. Any conduit used does 
not then need to be earthed. 
2 The earthing conductor is insulated from the conduit. 



ANNEX B 
(Clause 3.1.3.2) 

REPRESENTATIVE VALUES OF SOIL RESISTIVITY IN VARIOUS PARTS OF INDIA 



SI 


Locality 


Type of Soil 


Order of 


Remarks 


No. 






Resistivity 
Q m 




(1) 


(2) 


(3) 


(4) 


(5) 



1 . Kakarapar, Distt Surat, Gujarat 

2. Taptee Valley 

3. Narmada Valley 



4. Purna Valley (Deogaon) 

5. Dhond, Mumbai 

6. Bijapur Distt, Karnataka 

7 . Garimenapenta, Distt Nellore 
Andhra Pradesh 

8. Kartee 

9. Delhi 

a) Najafgarh 



b) Chhatarpur 



Clayey black soil 6-23 

Alluvium 6-24 

Alluvium 4-11 



Agricultural 3-6 

Alluvium 6-40 

a) Black cotton soil 2-10 

b) Moorm 10-50 
Alluvium (highly 2 
clayey) 

a) Alluvium 3-5 

b) Alluvium 9-21 

a) Alluvium 75-170 
(dry sandy soil) 

b) Loamy to clayey 38-50 
soil 

c) Alluvium (saline) 1.5-9 
Dry soil 36-109 



Underlying 
trap 



bedrock-Deccan 



do 



Underlying bedrock-sand- 
stone shale and lime-stones, 
Deccan trap and gneisses 
Underlying bedrock-Deccan 
trap 

do 

do 

do 
Underlying bedrock-gneisses 

Underlying bedrock- sand- 
stone, trap or gneisses 



do 

do 

do 
Underlying bedrock- 
quartzites 



154 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



SI 


Locality 


Type of Soil 


Order of 


Remarks 


No. 






Resistivity 
Q m 




(1) 


(2) 


(3) 


(4) 


(5) 


10. 


Korba, M.P. 


a) Moist clay 

b) Alluvium soil 


2-3 
10-20 


Underlying bedrock-sand- 
stone or shale 


11. 


Cossipur, Kolkata 


Alluvium 


25 
(approx) 


— 


12. 


Bhagalpur, Bihar 


a) Alluvium 


9-14 


Underlying bedrock-traps, 
sand-stone or gneisses 


13. 


Kerala (Trivandrum Distt) 


Lateritic clay 


2-5 


Underlying bedrock-laterite, 
charnockite or granites 


14. 


Bharatpur 


Sandy loam (saline) 


6-14 


— 


15. 


Kalyadi, Mysore 


Alluvium 


60-150 


Underlying bedrock-gneisses 


16. 


Kolar Gold Fields 


Sandy surface 


45-185 


do 


17. 


Wajrakarur, Andhra Pradesh 


Alluvium 


50-150 


do 


18. 


Koyana, Satara Distt 


Lateritic 


800-1 200 

(dry) 


Underlying bedrock-sand- 
laterite or trap 


19. 


Kutch-Kandla (Amjar Area) 


a) Alluvium (clayey) 


4-50 


Underlying bedrock-sand- 
stone, shale or tap 






b) Alluvium (sandy) 


60-200 


do 


20. 


Villupuram, Chennai 


Clayey sands 


11 


Underlying bedrock-granite 


21. 


Ambaji, Banaskantha, Gujarat 


Alluvium 


170 


Underlying bedrock-granites 
and gneisses 


22. 


Ramanathapuram Distt, Chennai 


a) Alluvium 


2-5 


Underlying bedrock-sand- 
stones and gneisses 






b) Lateritic soil 


300 
(approx) 


do 


NOTE — The soil resistivities are subject to wide seasonal variation as they depend 


very much on t 


he moisture content. 



PART 1 GENERAL AND COMMON ASPECTS 



155 



SP 30 : 2011 



ANNEX C 
(Clause 10.1) 

CASCADING, DISCRIMINATION AND LIMITATION 



C-l CASCADING 



The utilization of the current limiting capacity of a 
circuit-breaker at a given point to enable installation 
of lower-rated circuit-breakers in branch is known as 
'cascading' or 'back-up protection*. The main 
(upstream) circuit-breakers acts as a barrier against 
short-circuit currents and branch (downstream) circuit- 
breakers with lower breaking capacities than the 
prospective short-circuit (at their point of installation) 
operate under their normal breaking conditions. The 
limiting circuit-breaker helps the circuit-breaker placed 
downstream by limiting high short-circuit currents thus 
enabling use of downstream circuit-breaker with a 
breaking capacity lower than the short-circuit current 
calculated at its installation point thus enabling 
economical selection of circuit-breakers. 

Cascading concerns all devices installed downstream 
of the circuit-breaker, and can be extended to several 
consecutive devices, even if they are used in different 
switchboards. The upstream device must have an 
ultimate breaking capacity greater than or equal to the 
assumed short-circuit current at the installation point. 
For downstream circuit-breakers, the ultimate breaking 
capacity to be considered is the ultimate breaking 
capacity enhanced by coordination. 

The association of the upstream and downstream circuit- 
breakers allows an increase in performance of the 
breakers. Thus, the electromagnetic, electrodynamic and 
thermal effects of short-circuit currents are reduced. 
Installation of a single limiting circuit-breaker alongwith 
lower rated circuit-breakers results in considerable 
economy and simplification of installation work. 

D } and D 2 are the two circuit-breakers (see Fig. 11). 



t(s) A ^ «i 



As soon as the two circuit-breakers trip (as from point 
/ B ), an arc voltage U AD] on separation of the contacts 
of D } is added to voltage ?7 AD2 and helps, by additional 
limitation, circuit-breaker D 2 to open. 

The association D x + D 2 allows an increase in 
performance of D 2 as shown in Fig. 12, which depicts, 

limitation curve of D 2 , 

enhanced limitation curve of D 2 by D v 

I cu D 2 enhanced by D v 

Annex A of IS/IEC 60947-2 defines coordination under 
short-circuit conditions between circuit-breaker and 
another short-circuit protective device (SCPD) 
associated in the same circuit and the tests to be 
performed. Cascading is normally verified by tests for 
critical points. The tests are performed with an 
upstream circuit-breaker D 2 with a maximum 
overcurrent setting and a downstream circuit-breaker 
D 2 with a minimum setting. 

C-2 LIMITATION 

C-2.1 The technique of limitation allows the circuit- 
breaker to considerably reduce short-circuit currents. 
It ensures attenuation of the harmful electromagnetic, 
thermal and mechanical effects of short-circuits and is 
the basis of the cascading technique. 

The assumed fault current / sc is the short-circuit current 
that would flow at the point of the installation where 
the circuit-breaker is placed, if there were no limitation. 
Since the fault current is eliminated in less than one 
half-period, only the first peak current (asymmetrical 
peak 7) is considered. This is a function of the 
installation fault cos 9. Reduction of this peak / to 




Fig. 1 1 Operation of Circuit-Breakers in Cascade 



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l 



V 



*cuD2 ^citBI enhanced 



h 



~h 



D 1 helps D 2 t e break tie current 

— LimltattoH of H 2 @n§iaEie@fi§ by Dj 

•- Limitation of D» 



Llmltatloii of D 4 



Fig. 12 Limitation Curves for Circuit-Breakers 




Fig. 13 Effect of Limitation on Fault Current 

limited I L characterizes circuit-breaker limitation. 
Limitation consists of creating a back-electromotive 
force opposing the growth of the short-circuit current. 
Effectiveness of limitation depends on intervention 
time, that is the time t s when the back-electromotive 
force (b cmf ) appears, the rate at which b tmi increases 
and the value of b cmf . The back-electromotive force is 
the arc voltage £/ a due to the resistance of the arc 
developing between the contacts on separation. Its 
speed of development depends on the contact separation 
speed. As shown in Fig. 13, as from the time t s when 
the contacts separate, the back less than the assumed 
fault current flow through when a short-circuit occurs. 

C-2.2 Circuit-Breaker Limitation Capacity 

The circuit-breaker limitation capacity defines the way 



how it reduces the let through current in short-circuit 
conditions (see Fig. 14 and 15). The thermal stress of the 
limited current is the area (shaded) defined by the curve 
of the square of the limited current I s 2 c (t) . If there is no 
limitation, this stress would be the area, far larger, that 
would be defined by the curve of the square of the assumed 
current. For an assumed short-circuit current I sc , limitation 
of this current to 10 percent results in less than 1 percent 
of assumed thermal stress. The cable temperature rise is 
directly proportional to the thermal stress. 

NOTE — On a short-circuit, adiabatic temperature-rise of 
conductors occurs (without heat exchange with the outside due 
to the speed of the energy supply). The increased temperature 
for a conductor with a cross-section S is: 



B . = jrvy* 



where I 2 dt is the thermal stress (A 2 s) 



100% -- 



— ^ss^— Assumed transient p@a§s I 



10% 




assumed st@ 
p#aw *„ 



_!a — limited peak J w 



w 



1 



Fig. 14 Current Limitation 




Assumed m iy100% 



Limited energy < 1% 



Fig. 15 Thermal Stress Limitation 

Limitation considerably attenuates the harmful effects 
of short-circuits on the installation. Consequently, 
limitation contributes to the durability of electrical 
installations. Due to limitation, the harmful effects of 
short-circuits on a motor feeder are greatly attenuated. 
Proper limitation ensures easy access to a Type 2 
coordination as per IS/IEC 60947-4-1, without 
oversizing of components. This type of coordination 
ensures optimum use of their motor feeders. 



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C-2.3 Limitation Curves 

A circuit-breaker's limiting capacity is expressed by 
limitation curves that give, 

a) the limited peak current as a function of the 
rms current of the assumed short-circuit 
current. For example on a 160 A feeder where 
the assumed lsc is 90 kA rms, the non-limited 
peak lsc is 200 kA (asymmetry factor of 2.2) 
and the limited 7 SC is 26 kA peak. 

b) the limited thermal stress (in A2s) as a 
function of the rms current of the assumed 
short-circuit current. For example, on the 
previous feeder, the thermal stress moves from 
more than 100 x 106 A2s to 6 x 106 A2s. 

C-3 DISCRIMINATION 

C-3.1 Discrimination is the co-ordination of the 
operating characteristics of two or more over-current 
protective devices such that, on the incidence of over- 
currents within stated limits, the device intended to 
operate within these limits does so, while the other(s) 
does (do) not (see Fig. 16). 

Distinction is made between series discrimination 
involving different over-current protective devices 
passing substantially the same over-current and 
network discrimination involving identical protective 
devices passing different proportions of the over- 
current. In LV networks, discrimination is 
recommended in order to obtain higher levels of supply 
continuity and protection, ensuring better safety of 
installations and minimum cost overruns. 

Cascading principle in limiting CBs can enhance the 
discrimination levels. It is recommended that the 
manufacturer provide the relevant data in terms of 
discrimination charts and cascading levels for various 
combination of CBs (upstream and downstream) and 
fault current as per the laboratory test results. 

A discrimination current 7 S is defined such that if; 

a) / fau]t > / s : both circuit-breakers trip, and 

b) / fault < 7 S : only D 2 eliminates the fault. 



C-3.2 Discrimination Quality 



i 



V 



^mmmmmmH^mmmmmm^ o 



I 






F®2 

D 2 oniy 

trips 

Fig. 16 Discimination and Sequence of Tripping 



The value J s is compared with assumed / sc (Z) 2 ) at point 
ft 

a) 



D 2 of the installation 



total discrimination: I s > 7 SC (D 2 ); 
discrimination is qualified as total, that is 
whatever the value of the fault current, D 2 only 
will eliminate it. 
b) partial discrimination: I s < 7 SC (7) 2 ); 
discrimination is qualified as partial, that is 
up to 7 S , only D 2 eliminates the fault. Beyond 
7 S , both 7), and D 2 open. 

where 

7 SC (£>,): short-circuit current at the point where 
D x is installed, 

7 CU Dj : ultimate breaking capacity of D } . 

C-3.3 Types of Discriminations 

C -3.3,1 Current Discrimination 

This technique is directly linked to the staging of the 
Long Time (LT) tripping curves of two serial-connected 
circuit-breakers (see Fig. 17). 



t(s) 




**ra *ri -*sda s«ii 



Fig. 17 Current Discrimination 

The discrimination limit 7 S is, 

a) 7 S = 7 sd2 if the thresholds 7 sd] and 7 sd2 are too close 
or merge, and 

b) ^ s = hdi^ tne thresholds 7 sdl and 7 sd2 are 
sufficiently far apart. 

Current discrimination is achieved when, 

a) / rl // r2 <2 

b) / sdl // sd2 >2 

The discrimination limit being 



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C-3.3.1.1 Discrimination quality 

Discrimination is total if / s > / SC (£> 2 X that is 7 S dl > / SC (D 2 ). 

This normally implies, 

a relatively low level I SC (D 2 ), 
a large difference between the ratings of circuit- 
breakers D ] and D r 

Current discrimination is normally used in final 
distribution. 

C -3.3.2 Time Discrimination 

This is the extension of current discrimination and is 
obtained by staging over time of the tripping curves. 
This technique consists of giving a time delay of t to 
the Short Time (ST) tripping of D x (see Fig. 18). 




Fig. 18 Time Discrimination 

The thresholds (7 rl , 7 sdl ) of D x and (7 r2 , 7 sd2 ) comply 
with the staging rules of current discrimination. The 
discrimination limit 7 S of the association is at least equal 
to 7 U , the instantaneous threshold of D v 

C-3.3.2.1 Discrimination quality 

For discrimination on final and/or intermediate feeders, 
A category circuit-breakers can be used with time- 
delayed tripping of the upstream circuit-breaker. This 
allows extension of current discrimination up to the 
instantaneous threshold I u of the upstream circuit- 
breaker: 7 S > 7 n . If 7 SC (D 2 ) is not too high (case of a 
final feeder) total discrimination can be obtained. 

On the incomers and feeders of the MSB, as continuity 
of supply takes priority, the installation characteristics 
allow use of B category circuit-breakers designed for 
time-delayed tripping. These circuit-breakers have a 
high thermal withstand (7 CW > 50 percent 7 cn for t = 7 S ): 
7 S > 7 cwl . Even for high 7 SC (D 2 ), time discrimination 
normally provides total discrimination: 7 cwi > 7 SC (D 2 ). 



NOTE — Use of B category circuit-breakers means that the 
installation must withstand high electrodynamic and thermal 
stresses. Consequently, these circuit-breakers have a high 
instantaneous threshold / k that can be adjusted and disabled in 
order to protect the busbars if necessary. 

C-3.4 Enhancement of Current and Time 
Discrimination 

C-3.4.1 Enhancement by Limiting Downstream 
Circuit-Breakers 

Use of a limiting downstream circuit-breaker enables 
the discrimination limit to be pushed back. 



noiHImltliig 




gt»rt*elreult 
limlter 



Fig. 19 Enhancement of Discrimination 

On referring to Fig. 19, a fault current / d will be seen 
by D l9 

equal to / d for a non-limiting circuit-breaker, and equal 
to 7 Ld < / d for a limiting circuit-breaker. 

The limit of current and time discrimination 7 S of the 
association D t + Z) 2 is thus pushed back to a value that 
increases when the downstream circuit-breaker is rapid 
and limiting. 

C-3.4.2 Discrimination Quality 

Use of a limiting circuit-breaker is extremely effective 
for achievement of total discrimination when threshold 
settings (current discrimination) and/or the 
instantaneous tripping threshold (time discrimination) 
of the upstream circuit-breaker D x are too low with 
respect to the fault current I d in D 2 - I SC (D 2 ). 

C-3.4.2. 1 Logic discrimination or "Logic 
Discrimination Zone (ZSI) " 

This type of discrimination can be achieved with 
circuit-breakers equipped with specially designed 
electronic trip units. Only the Short Time Protection 
(STP) and Ground Fault Protection (GFP) functions 
of the controlled devices are managed by Logic 
Discrimination. In particular, the Instantaneous 
Protection function (inherent protection function) is 
not concerned. 



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i 



pilot wir@ 



i 



Interlocking 



m4m 



I 



r 



gnt©r8oegcB«i 

I 



Fig. 20 Logic Discrimination(ZSI) 

C-3.4.2.2 Settings of controlled circuit-breakers 

a) Time delay: staging (if any) of the time delays 
of time discrimination to be applied (t D { > 
t D 2 > t D 3 ) 

b) Thresholds: natural staging of the protection 
device ratings must be complied with (7 cr Dj > 

'cA>'cA)- 

NOTE — This technique ensures discrimination even with 
circuit-breakers of similar ratings. 

C -3.4.2.3 Principles 

Activation of the Logic Discrimination function is via 
transmission of information on the pilot wire for ZSI 
input, 

a) Low level (no downstream faults): the 
Protection function is on standby with a 
reduced time delay (< 0.1) 

b) High level (presence of downstream faults): 
the relevant Protection function moves to the 
time delay status set on the device. 

Activation of the Logic Discrimination function is via 
transmission of information on the pilot wire for ZSI 
output, 

a) Low level: the trip unit detects no faults and 
sends no orders. 

b) High level: the trip unit detects a fault and 
sends an order. 

C-3.4.2.4 Operation 

A pilot wire connects in cascading form the protection 
devices of an installation (see Fig. 20). When a fault 
occurs, each circuit-breaker upstream of the fault 
(detecting a fault) sends an order (high level output) 
and moves the upstream circuit-breaker to its natural 
time delay (high level input). The circuit breaker placed 
just above the fault does not receive any orders (low 
level input) and thus trips almost instantaneously. 



C-3A2.5 Discrimination quality 

This technique enables easy achievement as standard 
of discrimination on 3 levels or more, easy achievement 
of downstream discrimination with non-controlled 
circuit-breakers, elimination of important stresses on 
the installation, relating to time-delayed tripping of the 
protection device, in event of a fault directly on the 
upstream busbars. All the protection devices are thus 
virtually instantaneous. 

C-3.5 Discrimination Rules 

C -3.5.1 Overload Protection 

For any overcurrent value, discrimination is guaranteed 
on overload if the non-tripping time of the upstream 
circuit-breaker D { is greater than the maximum 
breaking time of circuit-breaker D 2 . 

The condition is fulfilled if the ratio of Long Time (LT) 
and Short Time (ST) settings is greater than 2. The 
discrimination limit 7 S is at least equal to the setting 
threshold of the upstream Short Time (ST) time delay. 

C-3.5.2 Short-circuit Protection 

C-3.5.2.1 Time discrimination 

Tripping of the upstream device Dj is time delayed by 
r, the conditions required for current discrimination 
must be fulfilled and the time delay t of the upstream 
device Dj must be sufficient for the downstream device 
to be able to eliminate the fault. Time discrimination 
increases the discrimination limit / s up to the 
instantaneous tripping threshold of the upstream 
circuit-breaker D { (see Fig. 21). 

Discrimination is always total if circuit-breaker D, is 
of category B, has an / cw characteristic equal to its 7 CU . 

Discrimination is total in the other cases if the 
instantaneous tripping threshold of the upstream 
circuit-breaker D l is greater than the assumed 7 SC in D 2 . 

C-3.5.2.2 Logic discrimination 

Discrimination is always total. 

C-3.5.2.3 General case 

There are no general discrimination rules. The time/ 
current curves clearly supply a value of 7 SC (limited or 
assumed) less than the Short Time tripping of the 
upstream circuit-breaker; discrimination is then total. 
If this is not the case, only tests can indicate 
discrimination limits of coordination, in particular 
when circuit-breakers are of the limiting type. The 
discrimination limit 7 S is determined by comparison of 
curves, 

a) in tripping energy for the downstream circuit- 
breaker, and 



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b) in non-tripping energy for the upstream 
circuit-breaker. 

The potential intersection point of the curves gives the 
discrimination limit I s . The manufacturers indicate in 
tables the tested performance of coordination. 

C-3.6 Earth Leakage Protection Discrimination 

C-3.6.1 According to the Earthing System, 
discrimination only uses coordination of overcurrent 
protection devices. When the insulation fault is treated 
specifically by earth leakage protection devices (for 
example in the TT system), discrimination of the 
residual current devices (RCDs) with one another must 
also be guaranteed. Discrimination of earth leakage 
protection devices must ensure that, should an 
insulation fault occur, only the feeder concerned by 
the fault is de-energized. The aim is to optimize energy 
availability. 




en ©2 



Fig. 21 Discrimination at Various Fault Currents 

C-3.6.2 Types of Earth Leakage Protection 
Discrimination 

C-3.6.2.1 Vertical discrimination 

In view of requirements and operating standards, 
discrimination must simultaneously meet both the time 
and current conditions (see Fig. 22). 



C-3.6.2. 1.1 Current condition 

The RCD must trip between / n and I n 12, where I n is the 
declared operating current. There must therefore exist 
a minimum ratio of 2 between the sensitivities of the 
upstream device and the downstream device. In 
practice, the standardized values indicate a ratio of 3. 

C-3.6.2.1. 2 Time condition 

The minimum non-tripping time of the upstream device 
must be greater than the maximum tripping time of 
the downstream device for all current values. 

NOTE — The tripping time of RCDs must always be less than 
or equal to the time specified in the installation standards to 
guarantee protection of people against indirect contacts. 



A 



k 



•A 



c> 



1 



°1\ 



o 



RESIDUAL 
CURRENT 



Fig. 22 Vertical Discrimination 

For the domestic area, standards IS 12640 (Part 1) 
(residual current circuit-breakers) and IS 12640 (Part 
2) (residual current devices) define operating times. 
The values in the table correspond to curves G and S. 
Curve G (General) correspond to non-delayed RCDs 
and S (Selective) to those that are voluntarily delayed 
(see Fig. 23). 

t(HiS) ii 



2@9 



s: 



500 



Fig. 23 Operating Time Curves 

C-3.6.2.2 Horizontal discrimination 

Sometimes known as circuit selection, it allows savings 
at the supply end of the installation of an RCD placed 
in the cubicle if all its feeders are protected by RCDs. 
Only the faulty feeder is de-energized, the devices 
placed on the other feeders do not see the fault (see 
Fig. 24). 



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k 



\ 



f 



\ 




1 
\ 



risidum. 

CURRENT 
DEVICE 



I 




RESIDUAL 
CURRENT 
DEVICE 



Fig. 24 Horizontal Discrimination 



Table 2 Standardized Values of Operating Times 



Type /„ 


h n 


Standardized Values of Operating 


Time and Non 


-operating Time (in s) at: 




lAn 


2Ia 


5Ia„ 


500A 




General instantaneous All values 
Selective >25 


All values 
>0.030 


0.3 
0.5 
0.13 


0.15 
0.2 
0.06 


0.04 
0.15 
0.05 


0.04 
0.15 
0.04 


Maximum operating time 
Maximum operating time 
Maximum operating time 



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SECTION 15 LIGHTNING PROTECTION 



FOREWORD 

For the purposes of the National Electrical Code, the 
fixed installation for lightning protection is considered 
part of the electrical installation design and constitutes 
a major area where the installation design engineer has 
to ensure proper coordination. 

This Section covers the essential design and 
construction details of lightning protective systems. It 
is, however, intended to serve only as a guide of general 
nature on the principles and practices in the protection 
of structures against lightning, and account has to be 
taken of several other local conditions such as 
variations in the architecture, topography of the region, 
atmospheric conditions, etc. 

Lightning protection of industrial installations which 
are categorized as hazardous, require special 
considerations. These are summarised in Part 7 of the 
Code. 

Assistance has been derived from IS 2309 : 1989 'Code 
of practice for the protection of buildings and allied 
structures against lightning (second revision)* for this 
Section. 

1 SCOPE 

1.1 This (Part 1/Section 15) of the Code covers 
guidelines on the basic electrical aspects of lightning 
protective systems for buildings and the electrical 
installation forming part of the system. 

1.2 Additional guidelines if any, for specific 
occupancies from the point of lightning protection are 
covered in respective sections of the Code. 

2 REFERENCES 

The following Indian Standards on lightning protection 
may be referred for further details: 



IS No. 
IS 2309 : 1989 



IS 15086 : Part 5/ 
IEC 60099-5 : 1996 



Title 

Code of practice for the protection 
of buildings and allied structures 
against lightning (second revision) 
Surge arresters : Part 5 Selection 
and application recommen- 
dations 



3 TERMINOLOGY 

For the purposes of this Section, the following 
definitions shall apply. 

3.1 Air Termination (Lightning Conductor) or Air 

Termination Network — Those parts of a lightning 



protective system that are intended to collect the 
lightning discharges from the atmosphere. 

3.2 Bonds — Electrical connection between the 
lightning protective system and other metal work, and 
between various portions of the latter. 

3.3 Down Conductors — Conductors which connect 
the air terminations with the earth terminations. 

3.4 Earth Terminations or Earth Terminations 
Network — Those part of the lightning protective 
system which are intended to distribute the lightning 
discharges into the general mass of the earth. All parts 
below the testing point in a down conductor are 
included in this term. 

3*5 Earth Electrodes — A metal plate, pipe or other 
conductor or any array of conductors electrically 
connected to the general mass of the earth; these 
include those portions of the earth terminations that 
make direct electrical contact with the earth. 

3.6 Fasteners — Devices used to fasten the conductors 
to the structures. 

3.7 Isoceraunic Level — It is the number of days in a 
year on which the thunder is heard in the particular 
region averaged over a number of years. 

3.8 Joints — The mechanical and electrical junctions 
between two or more portions of the lightning 
protective system or other metal bonded to the system 
or both. 

3.9 Lightning Protective System — The whole system 
of interconnected conductors used to protect a structure 
from the effects of lightning. 

3.10 Metal-clad Building — A building with sides 
made of or covered with sheet metal. 

3.11 Metal-roofed Building — A building with roof 
made of or covered with sheet metal. 

3.12 Side Flash — A spark occurring between nearby 
metallic objects or between such objects and the 
lightning protective system or to earth. 

3.13 Testing Points — Joints in down conductors or 
in bonds or in earth conductors connecting earth 
electrodes, so designed and situated as to enable 
resistance measurements to be made. 

3.14 Zone of Protection — The space within which 
the lightning conductor is expected to provide 
protection against a direct lightning stroke. 

4 EXCHANGE OF INFORMATION 

4.1 The architect should exchange information with 



PART 1 GENERAL AND COMMON ASPECTS 



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SF 30 : 2010 



the engineer concerned when the building plans are 
being prepared. The primary object of such an 
exchange is to obtain information regarding the 
architectural features of the structure so that due 
provision may be made to retain the aesthetic features 
of the building while planning the location of the 
lightning conductors and down conductors of the 
lightning protective system. Information may also be 
obtained at an early stage regarding other services, such 
as electrical installation, gas and water pipes as well 
as climatic and soil conditions. 

4»2 Scale drawings showing plans and elevations of 
the structure should be obtained, and the nature, size 
and position of all the metal component parts of the 
lightning protective system should be indicated on 
them. In addition, a ground plan should show all the 
tall objects, such as, buildings, masts, transmission 
towers, tall trees, etc, within the zone of protection. 

5 CHARACTERISTICS OF LIGHTNING 
DISCHARGES 

5.1 The principal effects of lightning discharge to 
structure are electrical, thermal and mechanical. These 
effects are determined by the current which is 
discharged into the structure. These currents are 
unidirectional and may vary in amplitude from a few 
hundred amperes to about 200 kA. The current in any 
lightning discharge rises steeply to its crest value in a 
few microseconds and decays to zero in a few 
milliseconds. Many lightning discharges consist of a 
single stroke but some others involve a sequence of 
strokes which follow the same path and which 
discharge separate currents of amplitude and duration 
as mentioned above. A complete lightning discharge 
may thus last a second or even longer. 

5.2 Electrical Effects 

The principal electrical effects of a lightning discharge 
are two-fold. 

5.2.1 The lightning current which is discharged to earth 
through the resistance of the lightning conductor and 
earth electrode provided for a lightning protective 
system, produces a resistive voltage drop which 
momentarily raises the potential of the protective 
system with respect to the absolute earth potential to a 
very high value. The lightning current also produces, 
around the earth electrode, a high voltage gradient 
which may be dangerous to persons and animals. 

5.2.2 The lightning current rises steeply to its crest 
value (approximate at the rate of 10 kA/ms) and as a 
first approximation may be regarded as equivalent to 
high frequency discharge. A vertical conductor of the 
dimensions generally used in a lightning protective 
system has an inductance of about 16 x 10" 5 H/100 m. 



The rate of rise of current in conjunction with the 
inductance of the discharge path produces an inductive 
voltage drop which would be added, with due regard 
to the time relationship, to the resistive (ohmic) voltage 
drop across the earthing system. 

5.3 Thermal Effects 

The thermal effect of lightning discharge results in rise 
in temperature of the conductor through which the 
lightning current is discharged to the earth. Although 
the amplitude of the lightning current may be very high, 
its duration is so short that the thermal effect on a 
lightning protective system is usually negligible. This 
ignores the fusing or welding effects which occur 
locally consequent upon the rupture of a conductor 
which was previously damaged or was of inadequate 
cross- sectional area. In practice the cross-sectional area 
of a lightning conductor is determined primarily by 
mechanical considerations. 

5.4 Mechanical Effects 

When a high electric current is discharged through 
parallel conductors which are in close proximity to each 
other, these are subjected to large mechanical forces. 
The lightning conductors should, therefore, be 
provided with adequate mechanical fixings. 

5.4.1 A different mechanical effect exerted by a 
lightning discharge is due to the fact that the air channel, 
that is, the space between the thunder cloud and the 
lightning conductor, along which the discharge is 
propagated, is suddenly raised to a very high 
temperature. This results in a strong air pressure wave 
which is responsible for damages to buildings and other 
structures. It is not possible to provide protection 
against such an effect. 

6 DETERMINATION OF THE NEED FOR 
PROTECTION 

6.1 Risk Index 

In determining how far to go in providing lightning 
protection for specific cases or whether or not it is 
needed at all, it is necessary to take into account the 
following factors: 

a) Usage of structure, 

b) Type of construction, 

c) Contents or consequential effects, 

d) Degree of isolation, 

e) Type of isolation, 

f) Height of structure, and 

g) Lightning prevalance. 

6. LI IS 2309 gives the details of various factors that 
affect the risk of the structure being struck and the 



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consequential effects of a stroke. Certain values called 
'index figures', have been assigned to these factors 
which help in arriving at an overall 'risk index' to serve 
as an aid to judging whether lightning protection. The 
examples of such structures are: 

a) those in or near which large number of people 
congregate. 

b) those concerned with the maintenance of 
essential public services, 

c) those in areas where lightning strokes are 
prevalent, 

d) very tall or isolated structures, 

e) structures of historic or cultural importance, 
and 

f) structures containing explosives and highly 
flammable materials. 

7 ZONE OF PROTECTION 

7.1 The zone of protection of a lightning conductor 
denotes the space within which a lightning conductor 
provides protection against a direct lightning stroke 
by diverting the stroke to itself. Examples of the 
protection of different types and shapes of buildings 
along with zone of protection provided by their 
lightning protective systems are given in 8.2 of 
IS 2309. 

8 MATERIALS AND DIMENSIONS 

8.1 Materials 

The materials of lightning conductors, down 
conductors, earth termination network, etc, of the 
protective system shall be reliably resistant to corrosion 
or be adequately protected against corrosion. The 
following materials are recommended: 

a) Copper — When solid or stranded copper 
wire or flat copper strips are used, they 
shall be of grade ordinarily required for 
commercial electrical work, generally 
designated as being of 98 percent 
conductivity when annealed. They shall 
conform to relevant Indian Standards. 

b) Copper-clad Steel — Where copper-clad 
steel is used, the copper covering shall 
be permanently and effectively welded 
to the steel core. The proportion of copper 
and steel shall be such that the 
conductance of the material is not less 
than 30 percent of the conductance of 
solid copper of the same total cross- 
sectional area. 

c) Galvanized Steel — If there is any 
difficulty in the use of copper or 



aluminium, galvanized steel of the same 
cross section as recommended for copper 
may be used, in line with the provisions 
of IS 2309. Where steel is used it shall 
be thoroughly protected against corrosion 
by a zinc coating. Galvanized steel may 
be preferred for some short life 
installations, such as exhibitions. Copper 
is preferred to galvanized iron where 
corrosive gases, industrial pollution or 
saltaden atmospheric conditions are 
encountered. 

d) Aluminium — Aluminium wire and strips 
are increasingly finding favour for use as 
lightning conductors in view of the fact 
that aluminium has a conductivity almost 
double that of copper mass for mass. 
When used, it shall be least 99 percent 
pure, of sufficient mechanical strength 
and effectively protected against 
corrosion. 

e) Alloys — Where alloys of metals are used 
they shall be substantially as resistant to 
corrosion as copper under similar 
conditions. 

NOTE — Aluminium should not be used 
underground or in direct contact with walls. 

8.2 Shapes and Sizes 

The recommended shape and minimum sizes of 
conductors for use above ground and below ground 
are given in Table 1 and Table 2 respectively. 

Table 1 Shapes and Minimum Sizes of Conductors 

for Use Above Ground 
{Clause 8.2) 



SI Material and Shape 

No. 

(1) (2) 



Minimum Size 

(3) 



i) Round copper wire or 6 mm diameter 
copper-clad steel wire 

ii) Stranded copper wire 50 mm 2 (or 7/3.00 mm diameter) 

iii) Copper strip 20 mm x 3 mm 

iv) Round galvanized iron wire 8 mm diameter 

v) Galvanized iron strip 20 mm x 3 mm 

vi) Round aluminium wire 9 mm diameter 

vii) Aluminium strip 25 mm x 3.15 mm 



8.3 Corrosion 

Where corrosion due to atmospheric, chemical, 
electrolytic or other causes is likely to impair any part 
of the lightning protective system, suitable precautions 
should be taken to prevent its occurrence. The contact 
of dissimilar metals is likely to initiate and accelerate 
corrosion unless the contact surfaces are kept 



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completely dry and protected against the ingress of 
moisture. 

Table 2 Shapes and Minimum Sizes of Conductors 

for Use Below Ground 

{Clause 8.2) 



SI 


Material and Shape 


Minimum Size 


No. 






0) 


(2) 


(3) 


i) 


Round copper wire or copper-clad 
steel wire 


8 mm diameter 


ii) 


Copper strip 


32 mm x 6 mm 


iii) 


Round galvanized iron wire 


10 mm diameter 


iv) 


Galvanized iron strip 


32 mm x 6 mm 



8.3.1 Dissimilar metal contacts can exist where a 
conductor is held by fixing devices or against external 
metal surfaces. Corrosion can arise also where water 
passing over one metal comes into contact with another. 
Run-off water from copper, copper alloys and lead can 
attack aluminium alloys and zinc. The metal of the 
lightning protective system should be compatible with 
the metal or metals used externally on the structure 
over which the system passes or with which it may 
make contact. 

9 DESIGN 

9.0 General 

Lightning protective systems should be installed with 
a view to offering least impedance to the passage of 
lightning current between air-terminals and earth. 
There shall be at least two parts, and more if practicable. 
This is done by connecting the conductors to form a 
cage enclosing the building. The basic design 
considerations for lightning protective systems are 
given in IS 2309. 

The principal component of a lightning protective 
system are: 

a) air terminations, 

b) down conductors, 

c) joints and bends, 

d) testing points, 

e) earth terminations, 

f) earth electrodes, and 

g) fasteners. 

9.1 Air Terminations 

For the purpose of lightning protection, the vertical 
and horizontal conductors are considered equivalent 
and the use of pointed air terminations or vertical finials 
is, therefore, not regarded as essential except when 
dictated by practical considerations. An air termination 
may consist for a vertical conductor as for a spire, a 



single horizontal and vertical conductors for the 
protection of bigger buildings. 

9.1.1 A vertical air termination need not have more 
than one point and shall project at least 30 cm above 
the object, salient point or network on which it is fixed. 

9.1.2 Horizontal air terminations should be so 
interconnected that no part of the roof is more than 9 
m away from the nearest horizontal conductor except 
that an additional 30 cm may be allowed for each 30 cm 
by which the part to be protected is below the nearest 
protective conductor. For a flat roof, horizontal air 
terminations along the outer perimeter of the roof are 
used. For a roof of building with larger horizontal 
dimensions a network of parallel horizontal conductors 
should be installed as shown in IS 2309. 

NOTE — Salient points even if less than 9 m apart should each 
be provided with an air termination. 

9.1.3 Horizontal air terminations should be coursed 
along contours, such as ridges, parapets and edges of 
flat roofs, and where necessary over flat surfaces in 
such a way as to join each air termination to the rest 
and should themselves form a closed network. 

9.1.4 The layout of the network may be designed to 
suit the shape of the roof and architectural features of 
the buildings. 

9.1.5 The air termination network should cover all 
salient points of the structure. 

9.1.6 All metallic finials, chimneys, ducts, vent pipes, 
railings, gutters and the like, on or above the main 
surface of the roof of the structure shall be bonded to, 
and form part of, the air termination network. If 
portions of a structure vary considerably in height, any 
necessary air termination or air termination network 
of the lower portions should, in addition to their own 
conductors, be bonded to the down conductors of the 
taller portions. 

9.1.7 All air terminals shall be effectively secured 
against overturning either by attachment to the object 
to be protected or by means of substantial braces and 
fixings which shall be permanently and rigidly attached 
to the building. The method and nature of the fixings 
should be simple, solid and permanent, due attention 
being given to climatic conditions and possible 
corrosion. 

9.2 Down Conductors 

The number and spacing of down conductors shall 
largely depend upon the size and shape of the building 
and upon aesthetic considerations. The minimum 
number of down conductors may, however, be decided 
on the following considerations: 



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a) A structure having a base area not exceeding 
1 00 m 2 may have one down conductor only if 
the height of the air termination provides 
sufficient protection. However, it is advisable 
to have at least two down conductors except 
for very small buildings. 

b) For structures having a base area exceeding 
100 m 2 , the number of down conductors 
required should be worked out as follows: 

1) One for the first 100 m 2 plus one more 
for every additional 300 m 2 or part 
thereof, or 

2) One for every 30 m of perimeter. 
The small of the two shall apply. 

c) For a structure exceeding 30 m in height 
additional consideration as given in IS 2309 
shall apply. 

9.2.1 Down conductors should be distributed round 
the outside walls of the structure. They shall preferably 
be run along the corners and other projections, due 
consideration being given to the location of air 
terminations and earth terminations. Lift shaft shall not 
be used for fixing down conductors. 

9.2.2 It is very important that the down conductors shall 
follow the most direct path possible between the air 
termination and the earth termination, avoiding sharp 
bends, upturns and kinks. Joints shall as far as possible 
be avoided in down conductors. Adequate protection 
may be provided to the conductors against mechanical 
damage. Metal pipes should not be used as protection 
for the conductors. 

9.2.3 Metal pipes leading rainwater from the roof to 
the ground may be connected to the down conductors 
but cannot replace them. Such connections shall have 
disconnecting joints for testing purposes. 

9.2.4 Where the provision of suitable external routes 
for down conductors is impracticable or inadvisable, 
as in buildings of cantilever construction, from the first 
floor upwards, down conductors may be used in an air 
space provided by a non-metallic non-combustible 
internal duct. Any covered recess not smaller 
than 75 mm x 15 mm or any vertical service duct 
running the full height of the building may be used for 
this purpose, provided it does not contain an 
unarmoured or non-metal- sheathed cable. 

9.2.5 Any extended metal running vertically through 
the structure should be bonded to the lightning 
conductor at the top and the bottom unless the clearance 
are in accordance with IS 2309 for tall structures. 

9.2.6 A structure on bare rock, should be provided with 
at least down conductors equally spaced. 



9.2.7 In deciding on the routing of the down conductor, 
its accessibility for inspection, testing and maintenance 
should be taken into account. 

9.3 Joints and Bonds 

9.3.1 Joints 

The lightning protective system shall have as few joints 
in it as necessary. In the down conductors below ground 
level these shall be mechanically and electrically 
effective and shall be so made as to exclude moisture 
completely. The joints may be clamped, screwed, 
bolted, crimped, riverted or welded. With overlapping 
joints the length of the overlap should not be less 
than 20 mm for all types of conductors. Contact 
surfaces should first be cleaned and then inhibited from 
oxidation with a suitable non-corrosive compound. 
Joints of dissimilar metal should be suitably protected 
against bimetallic action and corrosion. 

9.3.1.1 In general, joints for strips shall be tinned, 
soldered, welded or brazed and at least double-riveted, 
welded or brazed and at least double-riveted. Clamped 
or bolted joints shall only be used on test points or on 
bonds to existing metal, but joints shall only be of the 
clamped or screwed type. 

9.3.2 Bonds 

External metal on or forming part of a structure may 
have to discharge the full lightning current. Therefore, 
the bond to the lightning protective system shall have 
a cross-sectional area not less than that employed for 
the main conductors. On the other hand, internal metal 
is not so vulnerable and its associated bonds are, at 
most, only likely to carry a portion of the total lightning 
current, apart from their function of equalizing 
potential. These latter bonds may, therefore, be smaller 
in cross-sectional area than those used for the main 
conductors. All the bonds should be suitably protected 
against corrosion. Bonds shall be as short as possible. 

9.4 Testing Points 

Each down conductor shall be provided with a testing 
point in a position convenient for testing but 
inaccessible for interference. No connection, other than 
one direct to an earth electrode, shall be made below a 
testing point. Testing points shall be phosphorbronze, 
gunmetal, copper or any other suitable material. 

9.5 Earth Terminations 

Each down conductor shall have an independent earth 
termination. It should be capable of isolation for testing 
purposes. Suitable location for the earth termination 
shall be selected after testing and assessing the specific 
resistivity of the soil and with due regard to reliability 
of the sub-soil water to ensure minimum soil moistness. 



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9.5.1 Water pipe system should not be bonded to the 
earth termination system. However, if adequate 
clearance between the two cannot be obtained, they 
may be effective bonded and the bonds should be 
capable of isolation and testing. The gas pipes, 
however, should in no case be bonded to the earth 
termination system. 

9.5.2 It is recommended that all earth terminations 
should be interconnected. Common earthing, besides 
equalizing the voltage at various earth terminations also 
minimizes any risk to it of mechanical damage. The 
condition for limiting earthing resistance given in 12 
does not apply and in such a case no provision need be 
made for isolation in earth. 

9.5.3 A structure standing on bare rock should be 
equipped with a conductor encircling and fixed to the 
structure at ground level and following reasonably 
closely the contour of the ground. This conductor 
should be installed so as to minimize any risk to it of 
mechanical damage. The condition for limiting 
earthing resistance given in 12 does not apply and in 
such a case no provision need be made for isolation in 
earth termination for testing. Where there is a risk to 
persons or to valuable equipment, expert advice should 
be sought. 

9,6 Earth Electrodes 

Earth electrodes shall be constructed and installed in 
accordance with Part 1/Section 14 of the Code. 

9.6.1 Earth electrodes shall consist of rods, strips or 
plates. Metal sheaths of cables shall not be used as 
earth electrodes. 

9.6.2 When rods or pipes are used they should be driven 
into the ground as close as practicable but outside the 
circumference of the structure. Long lengths in sections 
coupled by screwed connectors or socket joints can be 
built up where necessary to penetrate the substrate of 
low resistivity. Where ground conditions are more 
favourable for the use of shorter lengths of rods in 
parallel, the distance between the rods should 
preferably be not less than twice the length of the rods. 
The arrangement of earth electrodes are given in Fig. 24 
of IS 2309. 

9.6.3 When strips are used, these should be buried in 
trenches or beneath the structure at a suitable depth, 
but not less than 0.5 m deep to avoid damage by 
building or agricultural operations. The strips should 
preferably be laid radially in two or more directions 
from the point of connection to a down conductor. But 
if this is not possible they may extend in one direction 
only. However, if the space restriction requires the strips 
to be laid in parallel or in grid formation the distance 
between two strips should not be less than 2 m. 



9.6.4 When plate electrodes are used they shall be 
buried into the ground so that the top edge of the plate 
is at a depth not less than 1.5 m from the surface of the 
ground. If two plate electrodes are to be used in parallel 
the distance between the two shall not be less than 8 m. 

9.6.5 In the neighbourhood of structure where high 
temperatures are likely to be the encountered in the 
sub-soil, for example brick kilns, the earth electrodes 
may have to be installed at such a distance from the 
structure where the ground is not likely to be dried 
out. 

9.7 Fasteners 

Conductors shall be securely attached to the building 
or other object to be protected by fastners which shall 
be substantial in construction, not subject to breakage, 
and shall be made of galvanized steel or other suitable 
material. If fasteners are made of steel, they should be 
galvanized to protect them against corrosion. If they 
are made of any other material suitable precautions 
should be taken to avoid corrosion. Some samples of 
fasteners are shown in IS 2309. 

9.8 Earth Resistance 

Each earth termination should have a resistance in 
ohms to earth not exceeding numerically the product 
of 10 and the number of earth terminations to be 
provided. The whole of the lightning protective system 
should have a combined resistance to earth not 
exceeding 10 ohms before any bonding has been 
effected to metal in or on the structure or to surface 
below ground. 

10 ISOLATION AND BONDING 

10.0 When a lightning protective system is struck with 
a lightning discharge, its electrical potential with 
respect to earth is raised, and unless suitable 
precautions are taken, the discharge may seek 
alternative paths to earth by side flashing to other metal 
in the structure. Side flashing may be avoided by the 
following two methods: 

a) Isolation, and 

b) Bonding. 

10.1 Isolation 

Isolation requires large clearances between the 
lightning protective system and other metal parts in 
the structure. To find out the approximate clearances, 
the following two factors should be taken into account: 

a) The resistive voltage drop in the earth 
termination, and 

b) The inductive voltage drop in the down 
conductors. 



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10.1*1 The resistive voltage drop requires a clearance 
of 0.3 m ohm of earthing resistance while the inductive 
voltage drop requires a clearance of 1 m for each 15m 
of structure height. For two or more down conductors 
with a common air termination this distance should be 
divided by the number of down conductors. The total 
clearance required is the sum of the two distances and 
may be expressed by the following simple equation: 



D = 03R 



H 

I5n 



where 

D 
R 

H 

n 



= required clearance in m; 

- combined earthing resistance of the earth 
termination, in ohms; 

= structure height in m, and 

= number of down conductors connected to a 
common air termination. 



10.1.2 The above clearance may be halved if a slight 
risk of occurrence of a side flash can be accepted. 

10.1.3 The drawback of isolation lies in obtaining and 
maintaining the necessary safe clearance and in 
ensuring that isolated metal has no connection via the 
water pipes or other services with the earth. In general, 
isolation can be practised only in small buildings. 

10.2 Bonding 

In structures which contain electrically continuous 
metal, for example, a roof, wall, floor or covering, this 
metal, suitably bonded, may be used as part of the 
lightning protective system, provided the amount and 
arrangement of the metal render it suitable for use in 
accordance with 9. 

10.2.1 If a structure is simply a continuous metal frame 
without external coverings it may not require any air 
termination or down conductors provided it can be 
ensured that the conducting path is electrically 
continuous and the base of the structure is adequately 
earthed. 

10.2.2 A reinforced concrete structure or a reinforced 
concrete frame structure may have sufficiently low 
inherent resistance to earth to provide protection 
against lightning and if connections are brought out 
from the reinforcement at the highest points during 
construction, a test may be made to varify this at the 
completion of the structure. 

10.2.3 If the resistance to earth of the steel frame of a 
structure or the reinforcement of a reinforced concrete 
structure is found to be satisfactory a suitable air 
termination should be installed at the top of the 
structure and bonded to the steel frame or to the 



reinforcement. Where regular inspection is not 
possible, it is recommended that a corrosion resistant 
material be used for bonding to the steel or to the 
reinforcement and this should be brought out for 
connection to the air termination. Down conductor and 
earth terminations will, of course, be required if the 
inherent resistance of the structure is found to be 
unsatisfactory when tested. 

10.2.4 Where metal exists in a structure as 
reinforcement which cannot be bonded into a 
continuous conducting network, and which is not or 
cannot be equipped with external earthing connections, 
its presence should be disgarded. The danger 
inseparable from the presence of such metal can be 
minimized by keeping it entirely isolated from the 
lightning protective system. 

10.2.5 Where the roof structure is wholly or partly 
covered by metal, care should be taken that such metal 
is provided with a continuous conducting path to earth. 

10.2.6 In any structure, metal which is attached to the 
outer surface or projects through a wall or a roof and 
has insufficient clearance from the lightning protective 
system, and is unsuitable for use as part of it, should 
preferably be bonded as directly as possible to the 
lightning protectives system. If the metal has 
considerable length (for example, cables, pipes, gutters, 
rain-water pipes, stair-ways, etc) and runs 
approximately parallel to a down conductor or bond, 
it should be bonded at each and but not below the test 
point. If the metal is in discontinuous lengths, each 
portion should be bonded to the lightning protective 
system; alternatively, where the clearance permits, the 
presence of the metal may be disregarded. 

10.-2,7 Bonding of metal entering or leaving a structure 
in the form of sheathing or armouring of cable, electric 
conduit, telephone, steam, compressed air or other 
services with earth termination system, should be 
avoided. However, if they are required to be bonded, 
the bonding should be done as directly as possible to 
the earth termination at the point of entry or exist 
outside the structure on the supply side of the service. 
The gap pipes should in no case be bonded with other 
metal parts. However, water pipes may be bonded to 
other metal parts, if isolation and adequate clearance 
cannot be obtained. In this operation all the statutory 
rules or regulations which may be in force should be 
followed and the competent authority should be 
consulted for providing lightning protection in such 
cases. 

10.2.8 Masses of metal in a building, such as bell-frame 
in a tower, should be bonded to the nearest down 
conductor by the most direct route available. 

10.2.9 Metal clading or curtain walling having a 



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continuous conducting path in all directions may be 
used as part of a lightning protective system. 

10.2.10 In bonding adjacent metalwork to the lightning 
protective system careful consideration should be given 
to the possible effects such bonding would have upon 
metalwork which may be cathodically protected. 

11 PROTECTION OF SPECIAL STRUCTURES 

For guidance on design of lightning protection systems 
for special structures, reference shall be made to 
IS 2309. Guidance for the appropriate authorities shall 
also be obtained. 

12 INSPECTION AND TESTING 

12.1 Inspection 

All lightning protective systems shall be examined by 
a competent engineer after completion, alteration or 
extensions, in order to verify that they are in accordance 
with the recommendations of the Code. A routine 
inspection shall be made at least once a year. 

12.2 Testing 

12.2.1 On completion of the installation or of any 
modification, the resistance of each earth termination 
or section thereof, shall, if possible, be measured and 
the continuity of all conductors and the efficiency of 
all bonds and joints shall be verified. 

12.2.2 Normally annual measurement of earth resistance 
shall be carried out but local circumstances in the light 
of experience may justify increase or decrease in this 
interval but it should not be less than once in two years. 
In the case of structures housing explosives or flammable 
materials, the interval shall be six months. 

12.2.3 Earth resistance shall be measured in accordance 
with Part 1/Section 14 of the Code. 



12.2.4 The actual procedure adopted for the test shall 
be recorded in detail so that future tests may be carried 
out under similar conditions. The highest value of 
resistance measured shall be noted as the resistance of 
the soil and details of salting or other soil treatment, 
should be recorded. 

12.2.5 The record shall also contain particulars of the 
engineer, contractor or owner responsible for the 
installation or upkeep or both of the lightning protective 
system. Details of additions or alterations to the system, 
and dates of testing together with the test results and 
reports, shall be carefully recorded. 

12.3 Deterioration 

If the resistance to earth of a lightning protective system 
or any section of it exceeds the lowest value obtained 
at the first installation by more than 100 percent, 
appropriate steps shall be taken to ascertain the causes 
and to remedy defects, if any. 

12.4 Testing Continuity and Efficacy of Conductors 
and Joints 

12.4.1 The ohmic resistance of the lightning protective 
system complete with air termination, but without the 
earth connection should be measured and this should 
be a fraction of an ohm. If it exceeds 1 ohm, then there 
shall be some fault either electrical or mechanical, 
which shall be inspected and the defect rectified. 

12.4.2 For this system is best divided into convenient 
sections at testing points by suitable joints. A 
continuous current of about 10 A shall be passed 
through the portion of the system under test and the 
resistance verified against its calculated or recorded 
value. Suitable portable precision testing sets for this 
purposes should be used. 



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SECTION- 16 PROTECTION AGAINST VOLTAGE SURGES 



FOREWORD 

A sudden change in the established operating 
conditions in an electrical network causes transient 
phenomena to occur. Transients may be generated 
outside of the home or business by lightning, other 
utility customers, animals, and even normal utility 
switching operations. Inside the home or business, 
transients are generated by motors starting and 
stopping, flourescent lighting, copiers, vending 
machines, welders, and many other sources. In a dry 
environment, electrical charges accumulate and create 
a very strong electrostatic field. Protection to mitigate 
the larger transients coming from outside the home or 
business, and point-of-use surge protection for 
equipment sensitive to transients generated within the 
building need to be considered. 

Assistance for this Section has been derived from 
IEC 61643-12-2008 'Low-voltage surge protective 
devices — Part 12: Surge protective devices connected 
to low-voltage power distribution systems — Selection 
and application principles'. 

1 SCOPE 

1.1 This Part 1/Section 16 covers the protection 
requirements in low voltage electrical installation of 
buildings. 

1.2 This part does not cover the primary protection 
against lightning which is covered under Part 1/ 
Section 15. 

2 REFERENCES 

A list of Indian Standards relevant to protection against 
voltage surges is given at Annex A. 

3 TERMINOLOGY 

The definitions given in Part 1 /Section 2 of this Code 
and the following shall apply. 

3.1 Continuous Operating Current (/ c ) — Current 
that flows in an SPD when supplied at its permament 
full withstand operating voltage (U c ) for each mode. I c 
corresponds to the sum of the currents that flow in the 
SPD's protection component and in all the internal 
circuits connected in parallel. 

3.2 Disruptive Discharge — The phenomena 
associated with the failure of insulation under electrical 
stress which include a collapse of voltage and the 
passage of current; the term applies to electrical 
breakdown in solid, liquid and gaseous dielectrics and 
combinations of these. 



NOTE — A disruptive discharge in a solid dielectric produces 
permanent loss of electrical strength; in a liquid or gaseous 
dielectric the loss maybe only temporary. 

3.3 Flashover — A disruptive discharge over a solid 
surface. 

3.4 Impulse — A unidirectional wave of voltage or 
current which, without appreciable oscillations, rises 
rapidly to a maximum value and falls, usually less 
rapidly, to zero with small, if any, loops of opposite 
polarity. The parameters which define a voltage or 
current impulse are polarity, peak value, front time, 
and time to half value on the tail. 

3.5 Impulse Current (/ imp ) — It is defined by a current 
peak value / peak and the charge a tested according to 
the test sequence of the operating duty test. This is 
used for the classification of the SPD for Class I test. 

3.6 Maximum Continuous Operating Voltage (U c ) 
— The maximum r.m.s. or d.c. voltage which may be 
continuously applied to the SPDs mode of protection. 
This is equal to the rated voltage. 

3.7 Maximum Discharge Current for Class II Test 
(J Max ) — Crest value of a current through the SPD 
having an 8/20 waveshape and magnitude according 
to the test sequence of the Class II operating duty test. 
W is g reater than 7 n- 

3.8 Nominal Discharge Current (/ n ) — The crest 
value of the current through the SPD having a current 
waveshape of 8/20. This is used for the classification 
of the SPD for the Class II test and also for 
pre-conditioning of the SPD for Class I and II tests. 

3.9 Puncture — A disruptive discharge through a solid. 

3.10 Rated Network Voltage (U n ) — The rated voltage 
of the network. 

3.11 Residual Voltage (t/ res ) — The peak value of the 
voltage that appears between the terminals of an SPD 
due to the passage of discharge current. 

3.12 Sparkover of an Arrester — A disruptive 
discharge between the electrodes of the gaps of an 
arrester. 

3.13 Surge Arrester — A device designed to protect 
electrical apparatus from high transient voltage and to 
limit the duration and frequently the amplitude of 
follow-current. The term 'surge arrester' includes any 
external series gap which is essential for the proper 
functioning of the device as installed for service, 
regardless of whether or not it is supplied as an integral 
part of the device. 



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NOTE — Surge arresters are usually connected between the 
electrical conductors of a network and earth although they may 
sometimes be connected across the windings of apparatus or 
between electrical conductors. 

3.14 Surge Protective Device (SPD) — A device that 
limits transient voltage surges and runs current waves 
to ground to limit the amplitude of the voltage surge 
to a safe level for electrical installations and 
equipment. Surge protective devices (SPDs) are used 
to protect, under specified conditions, electrical 
systems and equipment against various overvoltages 
and impulse currents, such as lightning and switching 
surges. 

3.15 Switching Overvoltages — These stresses are 
usually lower than lightning stresses in terms of peak 
current and voltage, but may have longer duration. 
However, in some cases, particularly deep inside a 
structure or close to switching overvoltage sources, the 
switching stress can be higher than the stresses caused 
by lightning. The energy related to these switching 
surges needs to be known to permit the choice of 
appropriate SPDs. The time duration of the switching 
surges, including transients due to faults and fuse 
operations, can be much longer than the lightning surge 
duration. 

3.16 Temporary Overvoltages (U T0X ) — Any SPD 
can be exposed to a temporary overvoltage U T0W during 
its lifetime that exceeds the maximum continuous 
operating voltage of the power system. A temporary 
overvoltage has two dimensions, magnitude and time. 
The time duration of the overvoltage primarily depends 
upon the earthing of the supply system (this includes 
both the high- voltage supply system as well as the low- 
voltage system to which the SPD is connected). In 
determining the temporary overvoltages, consideration 
should be given to the maximum continuous operating 
voltage of the power system (l/ cs ). 

3.17 Voltage Protection Level (U p ) — A parameter 
that characterizes the performance of the SPD in 
limiting the voltage across its terminals, which is 
selected from a list of preferred values. This value shall 
be greater than the highest value of the measured 
limiting voltages. 

The most common values for a 230/400 V network 
are: 

1 kV -1.2 kV -1.5 kV -1.8 kV - 2 kV - 2.5 kV 

3.18 Voltage Surge — A voltage impulse or wave 
which is superposed on the rated network voltage (see 
Fig. 1). A voltage surge disturbs equipment and causes 
electromagnetic radiation. The duration of the voltage 
surge (T) causes a surge of energy in the electrical 
circuits which is likely to destroy the equipment. 



4 GENERAL 

4.1 Voltage Surges 

A voltage surge disturbs equipment and causes 
electromagnetic radiation. Furthermore, the duration 
of the voltage surge (T) causes a surge of energy in the 
electrical circuits which is likely to destroy the 
equipment. There are four types of voltage surges 
which may disturb electrical installations and loads: 

a) Atmospheric voltage surges, 

b) Operating voltage surges, 

c) Transient overvoltage at industrial frequency, 
and 

d) Voltage surges caused by electrostatic 
discharge, 

4.1.1 Atmospheric Voltage Surges 

Atmospheric voltage surges, that is, lightning, comes 
from the discharge of electrical charges accumulated 
in the cumulo-nimbus clouds which form a capacitor 
with the ground. Storm phenomena cause serious 
damage. Lightning is a high frequency electrical 
phenomenon which produces voltage surges on all 
conductive elements, and especially on electrical loads 
and wires. Protection against lightning is covered under 
Part 1 /Section 15. 

4.1.2 Operating Voltage Surges 

A sudden change in the established operating 
conditions in an electrical network causes transient 
phenomena to occur. These are generally high 
frequency or damped oscillation voltage surge waves 
(see Fig. 1). 

They are said to have a slow gradient — their frequency 
varies from several ten to several hundred kilohertz. 

Operating voltage surges may be created by: 

The opening of protection devices (fuse, circuit- 
breaker), and the opening or closing of control devices 
(relays, contactors, etc). 

Inductive circuits due to motors starting and stopping, or 
the opening of transformers such as MVILV substations 

Capacitive circuits due to the connection of capacitor 
banks to the network 

All devices that contain a coil, a capacitor or a transformer 
at the power supply inlet: relays, contactors, television 
sets, printers, computers, electric ovens, filters, etc. 

4.1.3 Transient Overvoltages at Industrial Frequency 

These overvoltages (see Fig. 2) have the same 
frequency as the network (50, 60 or 400 Hz); and can 
be caused by: 



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VOLTAGE 



LIGHTING TYPE IMPULSE 

( duration = 100JL/S) 

(Operating impulse) 
type dumped ring wave 
F-IQQkHzl MHz) 




Trms 



Fig. 1 Voltage Surge Examples 



VOLTAGE (V or kV) 

i 




50% 






Voltage surge duration (T) 



Fig. 2 Transient Overvoltage at Industrial Frequency 



a) Phase/frame or phase/earth insulating faults on 
a network with an insulated or impedant neutral, 
or by the breakdown of the neutral conductor. 
When this happens, single phase devices will 
be supplied in 400 V instead of 230 V. 

b) A cable breakdown, for example a medium 
voltage cable which falls on a low voltage line. 

c) The arcing of a high or medium voltage 
protective spark-gap causing a rise in earth 
potential during the action of the protection 
devices. These protection devices follow 
automatic switching cycles which will 
recreate a fault, if it persists, 

4.1.4 Voltage Surges Caused by Electrical Discharge 

In a dry environment, electrical charges accumulate 
and create a very strong electrostatic field. For example, 
a person walking on carpet with insulating soles will 
become electrically charged to a voltage of several 



kilovolts. If the person walks close to a conductive 
structure, he will give off an electrical discharge of 
several amperes in a very short rise time of a few 
nanoseconds. If the structure contains sensitive 
electronics, a computer for example, its components 
or circuit boards may be damaged. 

4.2 Main Characteristics of Voltage Surges 

The surge protective device includes one or several 
non-linear components. The surge protective device 
eliminates voltage surges: 

a) In common mode : Phase to earth or neutral to 
earth. 

b) In differential mode: Phase to phase or phase 
to neutral. 

When a voltage surge exceeds the U c threshold, the 
surge protective device (SDP) conducts the energy to 
earth in common mode. In differential mode the 



PART 1 GENERAL AND COMMON ASPECTS 



173 



SP 30 : 2011 



diverted energy is directed to another active conductor 
(see Annex B). Table 1 sums up the main characteristics 
of voltage surges. 

The surge protective device has an internal thermal 
protection device which protects against burnout at its 
end of life. Gradually, over normal use after 
withstanding several voltage surges, the SPD degrades 
into a conductive device. An indicator informs the user 
when end-of-life is close. 

Some surge protective devices have a remote 
indication. In addition, protection against short-circuits 
is ensured by an external circuit-breaker. 

4.3 Basic Functions of Surge Protection Devices 
(SPDs) 

The functions of surge protection devices are as 
follows: 

a) In power systems in the absence of surges: 
the SPD shall not have a significant influence 
on the operational characteristics of the 
system to which it is applied. 

b) In power systems during the occurrence of 
surges: the SPD responds to surges by 
lowering its impedance and thus diverting 
surge current through it to limit the voltage 
to its protective level. The surges may initiate 
a power follow current through the SPD. 

c) In power systems after the occurrence of 
surges: the SPD recovers to a high-impedance 
state after the surges and extinguishes any 
possible power follow current. 

The characteristics of SPDs are specified to achieve 
the above functions under normal service conditions. 
The normal service conditions are specified by the 
frequency of the power-system voltage, load current, 
altitude (that is, air pressure), humidity and ambient 
air temperature. 

4.4 Surge Protective Device Tests 

4.4.1 Three test classes are defined for surge protective 



devices connected to low-voltage power distribution 
systems: 

a) Class I tests: They are conducted using 
nominal discharge current (/ n ), voltage 
impulse with 1.2/50 us waveshape and 
impulse current / imp . 

The Class I tests is intended to simulate 
partial conducted lightning current impulses. 
SPDs subjected to Class I test methods are 
generally recommended for locations at 
points of high exposure, for example line 
entrances to buildings protected by lightning 
protection systems. 

b) Class II tests: They are conducted using 
nominal discharge current (7 n ), voltage 
impulse with 1.2/50 us waveshape. 

c) Class HI tests: They are conducted using the 
combination waveform (1.2/50 and 8/20 us). 

4.4.2 SPDs tested to Class II or III test methods are 
subjected to impulses of shorter duration. These SPDs 
are generally recommended for locations with lesser 
exposure. SPDs are classified in the following three 
categories: 

a) Type 1 : SPD tested to Class I, 

b) Type 2: SPD tested to Class II, and 

c) Type 3 : SPD tested to Class III. 

4.4.3 The SPD is characterised by J7 C , l/ p , I n and 7 Max 
(see Fig. 3). 

4.4.4 To test the surge arrester, standardized voltage 
and current waves have been defined Voltage wave for 
example, 1.2/50 us (see Fig. 4) Current wave for 
example, 8/20 us (see Fig. 5). 

Other possible wave characteristics 4/10 jus, 10/1 000 us, 
30/60 us, 10/350 us. 

Comparison between different surge protective devices 
must be carried out using the same wave characteristics, 
in order to get relevant results. 



Table 1 Characteristics of Voltage Surges 
(Clause 4.2) 



SI No. 

(1) 


Type of Voltage Surge 

(2) 


Voltage Surge Coefficient 

(3) 


Duration 

(4) 


Front Gradient or 
Frequency 

(5) 


i) 


Industrial frequency (insulation fault) 


<1.7 


Long 

30 to 1 000 ms 


Industrial frequency 
(50-60-400 Hz) 


ii) 
iii) 


Operation 
Atmospheric 


2 to 4 
>4 


Short 

1 to 100 ms 

Very short 

1 to 100 us 


Average 
1 to 200 kHz 
Very high 

1 to 1 000 kV/^is 



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<1 RtA 



Fig. 3 Voltage/Current Characteristics 




Fig. 4 1.2/50 ps Wave 




Fig. 5 8/20 jus Wave 

5 SELECTION OF PROTECTION DEVICE 

5.1 For the selection of protection device, the value of 
the equipment to be protected should be estimated. To 
estimate its value, the cost of the equipment in financial 
terms and the economic impact if the equipment goes 
down needs to be taken into account. Protection devices 
shall be selected according to their environmental 
conditions and the acceptable failure rate of the 
equipment and the protective device. These factors 
include equipment to be protected and system 
characteristics, insulation levels, overvoltages, method 
of installation, location of SPDs, co-ordination of 
SPDs, failure mode of SPDs and equipment failure 
consequences etc. 

5.2 Rated residual voltage i/ res of protection devices 
must not be higher than the value in the voltage impulse 
withstand category II (see Table 2). 



5.3 Choice of Disconnector 

The disconnector is necessary to ensure the safety of 
the installation. 

One of the surge arrester parameters is the maximum 
current (/ Max 8/20 jis wave) that it can withstand without 
degradation. If this current is exceeded, the surge 
arrester will be destroyed; it will be permanently short 
circuited and it is essential to replace it. 

The fault current must therefore be eliminated by an 
external disconnector installed upstream. 

The disconnector provides the complete protection 
required by a surge arrester installation, that is: 

a) it must be able to withstand standard test 
waves: 

1 ) it must not trip at 20 impulses at 7 n , and 

2) it can trip at 7 Max without being destroyed. 

b) the surge arrester disconnects if it short- 
circuits. 

Surge arrester/disconnection circuit breaker 
correspondence table are generally supplied by 
manufacturers. 

5.4 Additional Requirements 

5.4.0 Depending upon the application of the SPD, 
additional requirements may be needed such as 
protection of SPDs against direct contact, safety in the 
event of SPD failures etc. An SPD may fail subjected to 
a surge greater than its designed maximum energy and 
discharge current capability. Failure modes of SPDs are 
usually divided into open-circuit and short circuit mode. 

5.4.1 End-of-life Indication of the Surge Arrester 

In the open-circuit mode the system to be protected is 
no longer protected. In this case, failure of an SPD is 
usually difficult to detect since it has almost no 
influence on the system. To ensure that the failed SPD 
is replaced before the next surge, an indication function 
may be required. Various indication devices are 
provided to warn the user that the loads are no longer 
protected against voltage surges. Many surge arresters 
have a light indicating that the module is in good 
working order. 

5.4.2 Use of Disconnecting Devices 

In the short-circuit mode, the system is severely 
influenced by the failed SPD. The short-circuit current 
flows through the failed SPD from the power source. 
Energy dissipated during the conduction of short circuit 
current may be excessive and cause a fire hazard. The 
short-circuit withstand capability test of covers this 
problem. In cases where the system to be protected 
has no suitable device to disconnect the failed SPD 



PART 1 GENERAL AND COMMON ASPECTS 



175 



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Table 2 Selection of Equipment for the Installation 
(Clause 5.2) 



SI No. 


Nominal Voltage of the Installation 




Required Impulse Withstand Voltage for 








V 






kV 










->*^. 






__^t^, ,„ 








Three-Phase 




Single-Phase 


Equipment at the 


Equipment at the 


Appliances 


Specially Protected 




Systems 




System with 
Middle Point 


Origin of the 
Installation 


Origin of the 
Installation 




Equipment 










(Impulse Withstand 


(Impulse Withstand 


(Impulse Withstand 


(Impulse Withstand 










Category IV) 


Category III) 


Category III) 


Category I) 


(1) 


(2) 




(3) 


(4) 


(5) 


(6) 


(7) 


i) 






120-240 


4 


2.5 


1.5 


0.8 


ii) 


230/400 

277/480 

(see Note 1) 






6 






1.5 


m 


400/690 




— 


8 


6 


4 


2.5 


iv) 


1000 




— 




Values subject to system engineers 





NOTES 

1 For voltages to earth higher than 300 V, the impulse withstand voltage corresponding to the next higher voltage in col (2) applies. 

2 Category I is addressed to particular equipment engineering. 

3 Category II is addressed to equipment for connection to the mains. 

4 Category III is addressed to installation material and some special products. 

5 Category IV is addressed to supply authorities and system engineers. 



from its circuit, a suitable disconnecting device may 
be required to be used in conjunction with a SPD which 
has a short-circuit failure mode. 

6 INSTALLATION OF SURGE PROTECTION 
DEVICES 

When installing surge protective devices, several 
elements must be considered, such as the earthing 
system, positioning with respect to residual current 
devices, the choice of disconnection circuit-breakers 
and cascading. 

6.1 Protection Devices According to the Earthing 
System 

a) Common mode overvoltage: Basic protection 
involves the installation of a common mode 
surge arrester between phase and PE or phase 
and PEN, whatever type of earthing system 
is used. 

b) Differential mode overvoltage: In the IT and 
TN-S earthing systems, earthing the neutral 
leads to dissymmetry due to earthing 
impedances, which causes differential mode 
voltages to appear, whereas the overvoltage 
induced by a lightning strike is a common 
mode voltage. 

6.2 Internal Architecture of Surge Arresters 

a) 2P, 3P, 4P surge arresters (see Fig. 6): 

They provide protection against common-mode 
overvoltages only and are appropriate for TN-C 
and IT earthing systems. 




Fig. 6 2P, 3P, 4P Surge Arresters 

b) 1P+N, 3P+N surge arresters (see Fig. 7): 

They provide protection against common-mode 
and differential-mode overvoltages and are 
appropriate for TT, TN-S, and IT earthing systems. 





Fig. 7 1P+N, 3P+N Surge Arresters 
c) Single-pole (IP) surge arresters (see Fig. 8). 

They are used to satisfy the demand of different 
assemblies (according to the manufacturer's 
instructions) by supplying only one product. 



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However, special dimensioning will be required for 
N-PE protection. 







Fig. 8 Connection Example 

6.3 Installation of Protection Devices 

The overvoltage protection study of an installation may 
show that the site is highly exposed and that the 
equipment to be protected is sensitive. The surge 
arrester must be able to discharge high currents and 
have a low level of protection. This dual constraint 
cannot always be handled by a single surge arrester. A 
second one will therefore be required (see Fig. 9). 

The first device, P x (incoming protection) will be 
placed at the incoming end of the installation. 




Fig. 9 Cascading of Surge Arresters 

Its purpose will be to discharge the maximum amount 
of energy to earth with a level of protection = 2 000 V 
that can be withstood by the electrotechnical equipment 
(contactors, motors, etc). 

The second device (fine protection) will be placed in a 
distribution enclosure, as close as possible to the 
sensitive loads. It will have a low discharge capacity 
and a low level of protection that will limit overvoltages 
significantly and therefore protect sensitive loads 
( = 1500 V). Cascading protection requires a minimum 



distance of at least 10 m between the two protection 
devices. This is valid whatever the field of application, 
domestic, tertiary or industrial. 

In Fig. 10, the fine-protection device P 2 is installed in 
parallel with the incoming protection device P l . 

If the distance L is too small, at the incoming 
overvoltage, P 2 with a protection level of U 2 = 1 500 V 
will operate before P x with a level of U x = 2 000 V. P 2 
will not withstand an excessively high current. The 
protection devices must therefore be coordinated to 
ensure that P x activates before P 2 . This depends on 
length L of the cable, that is the value of the self- 
inductance between the two protection devices. This 
self-inductance will block the current flow to P 2 and 
cause a certain delay, which will force P x to operate 
before P 2 . A metre of cable gives a self inductance of 
approximately 11 JH. 

The rule AU= Ldi/dt causes a voltage drop of 
approximately 100 V/m/kA, 8/20 jus wave. 

For L = 10 m, we get UL X = UL 2 =1 000 V. 

To ensure that P 2 operates with a level of protection of 
1 500 Y requires 

U x = UL X + UL 2 +£/ 2 =1000V+1000V+l 500 V 
= 3 500 V. 

Consequently, P x operates before 2 000 V and therefore 
protects P 2 . 

NOTE — If the distance between the surge arrester at the 
incoming end of the installation and the equipment to be 
protected exceeds 30 m, cascading the surge arresters is 
recommended, as the residual voltage of the surge arrester may 
rise to double the residual voltage at the terminals of the 
incoming surge arrester; as in the above example, the fine 
protection surge arrester must be placed as close as possible to 
the loads to be protected. It should be ensured that the 
connection between the surge arrester and its disconnection 
circuit breaker does not exceed 50 cm. 

6.4 Surge Protection Device Installation Conditions 

a) According to supply system configuration: 
The maximum continuous operating voltage 
U c of SPDs shall be equal to or higher than 
shown in Table 3. 

b) At the origin of the installation: If the surge 
arrester is installed at the source of an 
electrical installation supplied by the utility 
distribution network, its rated discharge 
current may be lower than 5 kA. 

If a surge arrester is installed downstream from 
an earth leakage protection device, an RCD of 
the S type, with immunity to impulse currents 
of less than 3 kA (8/20 jus), must be used. 

c) Protection against overcurrent at 50 Hz and 
consequences of a SPD failure: Protection 



PART 1 GENERAL AND COMMON ASPECTS 



177 



SP 30 : 2011 



UL1 





r UL2 P 

Fig. 10 Coordination of Surge Arresters 



against SPDs short-circuits is provided by the 
overcurrent protective devices which are to 
be selected according to the maximum 



recommended rating for the overcurrent 
protective device given in the manufacturer's 
SPD instructions. 



Table 3 Minimum Required U c of the SPD Dependent on Supply System Configuration 

(Clause 6.4) 



SI SPDs Connected 




System Configuration of Distribution Network 










_^*^ 






TT 


TN-C 


TN-S IT with Distributed 
Neutral 


IT without 
Distributed Neutral 


(1) (2) 


(3) 


(4) 


(5) (6) 


(7) 


i) Line conductor and neutral 


1.1 Uo 


Not applicable 


1.1 Uo 1.1 Uo 


Not applicable 


conductor 










ii) Each line conductor and PE 


1.1 Uo 


Not applicable 


1.1 Uo 3 Uo 


Line-to-the voltage 


conductor 






(see Note 3) 


(see Note 3) 


iii) Neutral conductor and PE 


Uo 


Not applicable 


Uo(l) Uo 


Not applicable 


conductor 


(see Note 3) 




(see Note 3) 




iv) Each line conductor and PEN 


Not applicable 


1.1 Uo 


NA NA 


Not applicable 


conductor 






(see Note 3) 





NOTES 

1 Uo is the line-to-neutral voltage of the low-voltage system. 

2 These values are related to worst case fault conditions, therefore the tolerance of 10 percent is not taken into account. 

3 In extended IT systems, higher values of U c may be necessary. 



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ANNEX A 
(Clause 2) 

LIST OF INDIAN STANDARDS RELEVENT TO PROTECTION AGAINST VOLTAGE SURGES 



IS No. 
732 : 1989 

2309 : 1989 
11548: 1986 



15086 (Part 1) : 
2001 

15086 (Part 3) : 

2003/IEC 

60099-3 : 1990 
15086 (Part 5): 

2001/IEC 

60099-5 : 1996 



Title 

Code of practice for electrical wiring 

installations 

Code of practice for the protection 

of buildings and allied structures 

against lightning 

Capacitors for surge protection for 

use in voltage system above 650 V 

and upto 33 kV 

Surge arresters: Part 1 Non-linear 

resistor type gapped surge arresters 

for ac systems 

Surge arresters: Part 3 Artificial 

pollution testing of surge arresters 

Surge arresters: Part 5 Selection 
and application recommendations 



IS No. 

QC 420100 : 
1994 /IEC QC 

420100 : 1991 
QC 420101 

: 1994 /IEC QC 

420101 : 1991 



QC 420102 : 
1993 /IEC QC 
420102 : 1991 



Title 

Varistors for use in electronic 
equipment — Sectional specification 
for surge suppression varistors 
Varistors for use in electronic 
equipment — Blank detail 
specification for silicon carbide surge 
suppression varistors assessment 
level E 

Varistors for use in electronic 
equipment — Blank detail 
specification for zinc oxide surge 
suppression varistors — Assessment 
level E 



ANNEX B 
(Clause 4.2) 

DIFFERENT PROPAGATION MODES OF VOLTAGE SURGE 



B-l COMMON MODE 

Common mode voltage surges occur between the live 
parts and the earth: phase/earth or neutral/earth 
(see Fig. 11), They are especially dangerous for devices 
whose frame is earthed due to the risk of dielectric 
breakdown. 



B-2 DIFFERENTIAL MODE 

Differential mode voltage surges circulate between live 
conductors: Phase to phase or phase to neutral 
(see Fig. 12). They are especially dangerous for 
electronic equipment, sensitive computer equipment, etc. 





Fig. 1 1 Common Mode 



Fig. 12 Differential Mode 



PART 1 GENERAL AND COMMON ASPECTS 



179 



SP 30 : 2011 

SECTION 17 GUIDELINES FOR POWER-FACTOR I IMPROVEMENT 



FOREWORD 

The various advantages of maintaining a high power 
factor of a system reflects on the national economy of 
a country. The available resources are utilized to its 
fullest possible extent. More useful power is available 
for transmission and utilization without any extra cost. 
Moreover, the life of individual apparatuses 
considerably increased and the energy losses reduced. 

Guidance to the consumers of electrical energy who 
take supply of low and medium voltage for 
improvement of power factor at the installation in their 
premises is provided in this Section. The guidelines 
provided are basically intended for installation 
operating at voltages below 650 V. For higher voltage 
installations, additional or more specific rules apply. 

Assistance has been derived from IS 7752 
(Part 1) : 1975 'Guide for the improvement of power 
factor in consumer installations: Part 1 Low and 
medium supply voltages'. 

1 SCOPE 

This Part 1 /Section 17 of the Code covers causes for 
low power factor and guidelines for use of capacitors 
to improve the same in consumer installations. 

1.2 Specific guidelines, if any, for individual 
installation on improvement of power factor are 
covered in the respective sections of the Code. 

2 REFERENCE 

The following Indian Standard on power factor 
improvement may be referred for details: 



IS 7752 (Part 1) : 
1975 



3 GENERAL 



Guide for the improvement of 
power factor in consumer 
installations: Part 1 Low and 
medium supply voltages 



3.1 Conditions of supply of electricity boards or 
licensees stipulate the lower limit of power factor which 
is generally 0.85 and consumer is obliged to improve 
and maintain the power factor of his installation to 
conform to these conditions. 

3.1.1 When the tariffs of Electricity Boards and the 
licensees are based on kVA demand or kW demand 
with suitable penalty rebate for low high power factor, 
improvement in the power factor would effect savings 
in the energy bills. 

3.2 Power factor is dependent largely on consumers' 
apparatus and partly on system components such as 



transformers, cables, transmission lines, etc. System 
components have fixed parameters of inductance, 
capacitance and resistance. The choice of these 
components to bring up the power factor depends on 
economics. 

3.3 In case of ac supply, the total current taken by 
almost every item of electrical equipment, except that 
of incandescent lighting and most forms of resistance 
heating, is made up of two parts, namely: 

a) in-phase component of the current (active or 
useful current) which is utilized for doing 
work or producing heat; and 

b) quadrature component of the current (also 
called 'idle' or 'reactive' current) and used 
for creating magnetic field in the machinery 
or apparatus. This component is not 
convertible into useful output. 

4 POWER FACTOR 

4.1 The majority of ac electrical machines and 
equipment draw from the supply an apparent power 
(kVA) which exceeds the required useful power (kW). 
This is due to the reactive power (kVAR) necessary 
for alternating magnetic field. The ratio of useful power 
(kW) to apparent power (kVA) is termed the power 
factor of the load. The reactive power is indispensable 
and constitutes an additional demand on the system. 

4.2 The power factor indicates the portion of the current 
in the system performing useful work. A power factor 
of unity (100 percent) denotes 100 percent utilization 
of the total current for useful work whereas a power 
factor of 0.70 shows that only 70 percent of the current 
is performing useful work. 

4.3 Principle Causes of Lower Power Factor 

4.3.1 The following electrical equipment and apparatus 
have a lower factor: 

a) Induction motors of all types particularly 
when they are underloaded, 

b) Power transformers and voltage regulators, 

c) Arc welders, 

d) Induction furnaces and heating coils, 

e) Choke coils and magnetic systems, and 

f) Fluorescent and discharge lamps, neon signs, 
etc. 

4.3.2 The principal cause of a low power factor is due 
to the reactive power flowing in the circuit. The reactive 
power depends on the inductance and capacitance of 
the apparatus. 



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4.4 Effect of Power Factor to Consumer 

4.4.1 The disadvantages of low power factor are as 

follows: 

a) Overloading of cables and transformer, 

b) Decreased line voltage at point of application, 

c) Inefficient operation of plant, and 

d) Penal power rates. 

4.4.2 The advantages of high power factor are as 
follows: 

a) Reduction in the current; 

b) Reduction in power cost; 

c) Reduced losses in the transformers and cables, 

d) Lower loading of transformers, switchgears, 
cables, etc; 

e) Increased capability of the 'power system' 
(additional load can be met without additional 
equipment); 

f) Improvement in voltage conditions and 
apparatus performance; and 

g) Reduction in voltage dips caused by welding 
and similar equipment. 

4.5 Economics of Power Factor Improvement 

4.5.1 Static capacitors, also called static condensers, 
when installed at or near the point of consumption, 
provide necessary capacitive reactive power, relieve 
distribution system before the point of its installation 
from carrying the inductive reactive power to that 
extent. 

4.5.2 The use of the static capacitors is an economical 
way of improving power factor on account of their 
comparatively low cost, ease of installation loss 
maintenance, low losses and the advantage of extension 
by addition of requisite units to meet the load growth. 
Installation of capacitors also improve the voltage 
regulation and reduces amperes loading and energy 
losses in the supply apparatus and lines. 

4.5.3 When considering the economics connected with 
power factor correction, it is most important to 
remember that any power factor improving equipment 
will, in general, compensate for losses and lower the 
loadings on supply equipment, that is, cables, 
transformers, switchgear, generating plant, etc. 

4.5.4 The minimum permissible power factor 
prescribed in the conditions of supply of Electricity 
Boards or Licensees and the reduction in charges 
offered in supply tariffs for further improvement of 
power factor shall, along with other considerations such 
as reduction of losses, etc, determine the kVAR 
capacity of the capacitors to be installed. 



4*5.5 In case of two port tariff with kVA demand 
charged, the value of economic improved power factor 
(cos <|> 2 ) may be obtained as follows: 

Let the tariff be Rs. A per kVA of maximum demand 
per annum plus Rs. P per kWh. 

cos (^ is the initial power factor, 

cos <t) 2 is the improved power factor after installing the 
capacitors 

The economic power factor cos (t> 2 is obtained from 
the expression 



B 

cos0 = Jl - 



where 



B = total cost per kVAR per year of capacitor 
installation inclusive of interest, depreciation 
and maintenance. 

NOTE — The explanation for the derivation of the 
formula for economic power factor cos f 2 is given in 
Annex A of IS 7752 (Parti). 

5 USE OF CAPACITORS 

5.1 In order to improve the power factor, the consumer 
shall install capacitors where the natural power factor 
of this installation is low. 

5.2 The average values of the power factor for different 
types of 3 phase electrical installations as measured 
by one of major utilities in the country are given in 
respective Sections of the Code. 

5.3 Capacitors for power factor improvement may be 
arranged as described in IS 7752 (Part 1). The 
successful operation of power factor improvement 
depends very largely on the positioning of the capacitor 
on the system. Ideal conditions are achieved when the 
highest power factor is maintained under all load 
conditions. 

5.4 Individual Compensation 

Wherever possible the capacitor should be connected 
directly across the terminals of the low power factor 
appliance or equipment. This ensures the control to be 
automatic through the same switching devices of the 
apparatus of appliance. 

5.5 Group Compensation 

In industries where a large number of small motors or 
other appliances and machines are installed and whose 
operation is periodical it is economical to dispense with 
individual installation of capacitors. A bank of 
capacitors may be installed to connect them to the 



PART 1 GENERAL AND COMMON ASPECTS 



181 



SP 30: 2011 



distribution centre of main bus-bars of the group of 
machines. 

5.6 Central Compensation 

Capacitors may also be installed at a central point, 
that is, at the incoming supply or service position. In 
order to overcome problems of drawing leading 
currents on light loads, these capacitors may be 
operated manually or automatically as required. The 
automatic control is preferred as it eliminates human 
errors. Automatic operation may be arranged by 
means of suitable relays in which a contractor controls 
the capacitors bank and maintains the correct amount 
of kVAR in the circuit. 

5.7 Combined Compensation 

Capacitors may be connected directly across the 
terminals of higher capacity inductive appliances or 
equipments, in addition to the capacitors with 
Automatic Power Factor Correction Relay for Central 
Compensation connected at the incoming supply or 
service position 

5.8 The methods of connecting power factor capacitors 
to supply line and motors are given in Fig. 1 and Fig. 2. 

6 SELECTION AND INSTALLATION OF 
CAPACITORS 

6.1 Capacitor current shall not exceed magnetization 
current of the motor when directly connected across 
motor terminals. 



6.2 Capacitors shall not be connected directly across 
motor terminals if solid state starters/soft starters are 
used. 

6.3 Capacitors shall not be connected directly to motor 
terminals if variable speed drive is adopted. 

6.4 Capacitors connected to same bus-bars discharge, 
instantaneously to uncharged capacitors, at the time 
of switching on, with high in-rush current. This shall 
be taken care of while providing central compensation 
with automatic power factor correction relay. 

6.5 Harmonics may reduce life of capacitors. 

6.6 Switching/controlling devices for capacitors shall 
have required capacitor switching duty. 

6.7 Chances of resonating shall be considered. 

6.8 Energy loss/Power consumption of capacitors shall 
be taken care of. 

6.9 Capacitor banks shall be properly ventilated. 

6.10 Chances of over voltage shall be looked into. 

6.11 Resistors shall be provided across capacitor 
terminals for discharging. 

7 POWER FACTOR IMPROVEMENT AND 
CAPACITOR RATING 

For calculating the size of the capacitor for power factor 
improvement reference should be made to Table 5 of 
Part 1/Section 20 of the Code. 



TO STARTER 





TO STAR DELTA 
STARTER 



Fig. 1 Methods of Connecting Capacitors to Motors for Improvement of Power Factor 
182 NATIONAL ELECTRICAL CODE 



SF 30 : 2011 



CIRCUIT BREAKER, 
CONTACTOR, OR 
FUSE SWITCH, AS 
RECOMMENDED 
( SUITABLE FOR 
GROUP OPERATION ) 



n 



060 



A^^jX,-^ 



^ 



ISOLATOR SWITCH 
X ^X „X TOBEOPENEDAT 
NO LOAD (SUITABLE 
FOR GROUP OPERATION) 



W% 



11 t v/ 



HRC FUSE 




Fig. 2 Methods of Connecting Capacitors to Supply Line for Improvement of Power Factor 



FART 1 GENERAL AND COMMON ASPECTS 



183 



SP 30: 2011 



SECTION 18 ENERGY EFFICIENCY ASPECTS 



FOREWORD 

Efficient use of energy inputs acquires added 
significance since energy saved is energy generated. 
Economic growth is desirable for developing countries 
and energy is essential for economic growth. This 
means commensurate input of energy is required. 
However, due to the fact that our fossil fuel reserves 
are limited, energy conservation is essential. Electrical 
energy input is utilized in various industrial plants, 
agricultural sector, commercial buildings and 
establishments, in the form of mechanical motive 
power, heating, lighting, air conditioning and 
ventilation etc. The Indian Industrial Sector accounts 
for half of the total commercial energy used in the 
country. Energy conservation aims at eliminating the 
waste of energy and minimization of losses. In this 
context proper selection of electrical equipment 
assumes greater importance. The Energy Conservation 
Act, 2001, also emphasises the need of energy 
conservation. 

This Section provides guidance to the consumers of 
electrical energy, with regard to the selection of 
equipment from energy conservation point of view and 
on energy audits. 

1 SCOPE 

This Part 1/Section 18 of the Code covers the aspects 
to be considered for selection of equipment from 
energy conservation point of view and guidance on 
energy audit. 

2 REFERENCE 

The following Indian Standard has been referred to in 
this Section: 



IS No 
IS 12615 : 2004 

3 GENERAL 



Title 

Energy efficient induction motors 
— Three phase squirrel cage 



Energy conservation aims at eliminating wastage of 
energy and minimizing losses. The major factors to be 
looked into in this regard include system design, 
selection of equipment, operation and maintenance 
practices, capacity utilization factors etc. Improving 
efficiency typically costs less than the energy tariffs. 

In order to standardize and benchmark the level of 
efficiency of various electrical and other energy 
consuming equipment, the Bureau of Energy Efficiency 
was instituted in March 2002. The standards and 



labelling/rating standards for various equipment 
proposed by Bureau of Energy Efficiency shall be 
followed while selecting equipment. Provisions of the 
Energy Conservation Act, 2001 may also be taken into 
account. 

4 EQUIPMENT SELECTION 

The main criterion for equipment selection, from 
energy conservation point of view, is that the power 
loss has to be minimum. In other words the operating 
efficiency should be high. Proper sizing of equipment 
is essential to ensure optimum utilization of energy. It 
is also necessary to avoid over rating or under rating 
the equipment. It should be ensured that operating 
power factor of equipment is high. 

Most commonly encountered equipments in electrical 
systems are mentioned below: 

4.1 Motor 

Motors should preferably be energy efficient motors, 
conforming to IS 12615. Preferably, motors shall 
conform to efficiency class 'eff V as per IS 12615 as 
these are more efficient than motors with efficiency 
class 'eff 2' . Motors with higher operating power factor 
shall be considered during selection as this results in 
lower current and consequently lower losses. Use of 
variable speed drives will bring substantial energy 
saving wherever different flow conditions/speeds are 
encountered in the process industry. Use of variable 
speed drives is a highly efficient means of achieving 
flow control etc. as compared to throttling of valves, 
dampers etc. or the use of stepped pulleys. 

4.2 Transformers 

While procuring transformers, normal loading shall be 
indicated so as to optimize transformer efficiency to 
be maximum at projected load for minimizing losses 
under normal operating conditions. Losses should be 
accounted while selecting equipment, by way of loss 
capitalization or specifying the minimum acceptable 
value for maximum efficiency. 

4.3 Cables Equipment 

Optimizing cable route/length can best reduce cable 
losses. Though the losses can also be reduced by over 
sizing the conductors, this is not recommended due to 
the practical problems encountered with termination 
of over sized cables. 

4.4 Lighting 

An efficient lighting system can substantially reduce 



184 



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SP 30 : 2011 



the energy consumption. The selection criteria for 
lighting shall include among other factors, luminaries 
with light sources of higher luminous efficiency such 
as tubular fluorescent as well as compact fluorescent 
lighting. Street lighting and other tasks where colour 
rendering properties of light are not of significance 
can be more efficiently achieved by the use of sodium 
vapour lamps compared to mercury vapour lamps. The 
use of incandescent lamps should be avoided except 
for DC lighting in critical areas such as escape routes. 
Newer technologies such as LED based lighting 
systems, building automation systems for optimizing 
power consumption through natural lighting, reduction 
in HVAC load demand through the use of solar films, 
lights controlled by sensors which get activated by 
movement/human presence etc. which can significantly 
optimize the use of electrical energy, also need to be 
promoted. The use of solar energy for lighting, heating 
etc. also needs to be maximized. 

Low loss electronic ballasts can be employed, where 
feasible, after taking care that the harmonic distortion 
is within permissible limits. 

5 ENERGY AUDIT 

5.1 'Energy Audit' means the verification, monitoring 
and analysis of the use of energy including submission 
of a technical report containing recommendations for 
improving energy efficiency with cost benefit analysis 
and an action plan to reduce energy consumption. 

5.2 The function of an energy audit broadly includes: 



— Review of level of energy consumption. 

— Creating a data base. 

— Identifying energy conservation potential. 

— Preparation of norms/guidelines for 
implementation of energy conservation 
measures. 

— Recommending the use of energy efficient 
appliances. 

5.3 Energy Conservation Act, 2001 has been enacted 
and the regulations issued under the said act shall be 
complied with, with reference to Energy Audit. 
Accordingly, designated consumers as notified under 
Energy Conservation Act, 2001, shall get the energy 
audit carried out through an accredited energy auditor/ 
firms and implement techno-economic viable 
recommendations/measures. Every designated consumer 
shall appoint or designate a certified energy manager, 
whose responsibility shall be to assist the designated 
consumer in complying with the energy consumption 
norms and standards and other mandatory provisions. 

5.4 Energy Conservation Building Code formulated 
by the Bureau of Energy Efficiency and prescribed by 
the Central Government shall be implemented for new 
buildings having connected load of 500 kW and above 
or contract demand of 600 kVA and above, once the 
same or modified version has been notified by the 
respective State Governments. List of energy intensive 
industries and other establishments specified as 
designated consumers is given in the Energy 
Conservation Act, 2001 . 



PART 1 GENERAL AND COMMON ASPECTS 



185 



SP 30: 2011 



SECTION 19 SAFETY IN ELECTRICAL WORK 



FOREWORD 

Safety procedures and practices are essential in 
electrical work. Basic approaches to electrical work 
from the point of view of ensuring safety which include 
inbuilt safety in procedures such as permit-to-work 
system, safety instructions and safety practices are 
covered in this Section. 

It is essential that safety should be preached and 
practiced at all times in the installation, operation and 
maintenance work. The real benefit to be derived from 
the guidelines covered in this Section will be realized 
only when the safety instructions it contains are 
regarded as normal routine duty and not as involving 
extra and laborious operations. 

1 SCOPE 

This Part 1 /Section 19 of the Code covers guidelines 
on safety procedures and practices in electrical work. 

2 REFERENCES 

A list of Indian Standards on safety in electrical work 
are as follows: 



IS No. 


Title 


2551 : 1982 


Specification for danger notice 




plates 


IS 5216 (Part 1) : 


Recommendations on safety 


1982 


procedures and practices in 




electrical work: Part 1 General 


IS 5216 (Part 2): 


Recommendations on safety 


1982 


procedures and practices in 




electrical work: Part 2 Life saving 




techniques 


8923 : 1978 


Warning symbol for dangerous 




voltages 


SP31 : 1986 


Method of treatment of electric 




shock 



3 PERMIT-TO-WORK SYSTEM 

3.1 All work on major electrical installations shall be 
carried out under permit-to-work system which is now 
well established, unless standing instructions are issued 
by the competent authority to follow other procedures. 
In extenuating circumstance, such as for the purpose 
of saving life or time in the event of an emergency, it 
may become necessary to start the work without being 
able to obtain the necessary permit-to-work; in such 
cases, the action taken shall be reported to the person- 
in-charge as soon as possible. The permit-to-work 
certificate from the person-in-charge of operation to 
the person-in-charge of the men selected to carry out 



any particular work ensure that the portion of the 
installation where the work is to be carried out is 
rendered dead and safe for working. All work shall be 
carried out under the personal supervision of a 
competent person. If more than one department is 
working on the same apparatus, a permit-to-work 
should be issued to the person-in-charge of each 
department. 

NOTE — The words 'permit-to-work' and 'permit' are 
synonymous for the purpose of this Section. 

3.2 No work shall be commenced on live mains unless 
it is specifically intended to be so done by specially 
trained staff. In such cases all possible precautions shall 
be taken to ensure the safety of the staff engaged for 
such work, and also of others who may be directly or 
indirectly connected with the work. Such work shall 
only be carried out with proper equipment provided 
for the purpose and, after taking necessary precautions, 
by specially trained and experienced persons who are 
aware of the danger that exists when working on or 
near live mains or apparatus. 

3.3 On completion of the work for which the permit- 
to-work is issued, the person-in-charge of the 
maintenance staff should return the permit duly 
discharged to the issuing authority. 

3.4 In all cases, the issue and return of permits shall be 
recorded in a special register provided for that purpose. 

3.5 The permits shall be issued not only to the staff of 
the supply undertakings, but also to the staff of other 
departments, contractors, engineers, etc, who might be 
required to work adjacent to live electrical mains or 
apparatus. 

3.6 A model form of permit-to- work certificate is given 
in IS 5216 (Parti). 

NOTES 

1 The permit is to be prepared in duplicate by the person-in- 
charge of operation on the basis of message, duly logged, from 
the person-in-charge of the work. 

2 The original permit will be issued to the person-in-charge of 
work and the duplicate will be retained in the permit book. 
For further allocation of work by the permit receiving officer, 
tokens may be issued to the workers authorizing them 
individually to carry out the prescribed work. 

3 On completion of the work, the original shall be returned to 
the issuing officer duly discharged for cancellation. 

3.7 Permit books should be treated as important 
records. All sheets in the permit books and the books 
themselves should be serially numbered. No page 
should be detached or used for any other except 
bonafide work. If any sheet is detached, a dated and 



186 



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SP 30 : 2011 



initiated statement shall then and there be recorded in 
the book by the person responsible for it. 

3.8 Permit books shall be kept only by the person-in- 
charge of operation who shall maintain a record of the 
receipts and issues made by him. 

4 SAFETY INSTRUCTIONS 

4.1 Safety Instructions for Working on Mains and 
Apparatus Up to and Including 650 Y 

4.1.1 Work on Dead Low and Medium Voltage Mains 
and Apparatus 

Unless a person is authorized to work on live mains 
and apparatus all mains and apparatus to be worked 
upon shall be isolated from all sources of supply before 
starting the work, proved dead, earthed and short- 
circuited. For earthing and short-circuiting, only 
recognized methods should be used. Measures shall 
be taken against, the inadvertent energizing of the 
mains and apparatus. 

4.1.2 Work on Live Mains and Apparatus 

Only competent, experienced and authorized persons 
shall work on live mains and apparatus, and such 
persons should take all safety measures as may be 
required. 

Warning boards shall be attached on or adjacent to the 
live apparatus and at the limits of the zone in which 
work may be carried out. 

Immediately before starting work, rubber gauntlets, if 
used, shall be thoroughly examined to see whether they 
are in sound condition. Under no circumstances shall 
be person work with unsound gauntlets, mass, stools, 
platforms or other accessories and safety devices. 

No live part should be within unsafe distance of a 
person working on live low and medium voltage mains 
so that he does not come in contact with it unless he is 
properly protected. 

4.1.3 Testing of Mains and Apparatus 

No person shall apply test voltage to any mains unless 
he has received a permit-to-work and has warned all 
persons working on the mains of the proposed 
application of test voltage. If any part which will thus 
become alive is exposed, the person-in-charge of the 
test shall take due precautions to ensure that the 
exposed live portion does not constitute danger to any 
person. It should also be ensured before the application 
of test voltage, that no other permit-to-work has been 
issued for working on this mains. 

4.1.4 Connecting Dead Mains to Live Mains 
When dead mains are connected to live mains, all 



connections to the live parts shall be made last, and in 
all cases the phase sequence should be checked to 
ensure that only like phases are connected together. 
Before inserting fuses or links in a feeder or distribution 
pillar controlling the cable on which a fault has been 
cleared, each phase shall first be connected through a 
test switch fuse. 

4.2 Safety Instructions for Working on Mains and 

Apparatus at Voltages Above 650 V 

4.2.1 General 

All mains and apparatus shall be regarded as live and 
a source of danger and treated accordingly, unless it is 
positively known to be dead and earthed. 

a) No person shall work on, test or earth mains 
or apparatus unless covered by a permit-to- 
work and after proving the mains dead except 
for the purpose of connecting the testing 
apparatus, etc. which is specially designed for 
connecting to the live parts. 

b) The operations of proving dead, earthing and 
short-circuiting of any mains shall be carried 
out only by an authorized person under the 
instructions of the person-in-charge of 
maintenance; 

c) While working on mains, the following 
precautions shall be taken: 

1) No person, after receiving a permit-to- 
work, shall work on, or in any way 
interfere with, any mains or conduits or 
through containing a live mains except 
under the personal instructions and 
supervision, on the site of work, of 
competent person, 

2) When any live mains is to be earthed, the 
procedure prescribed in 4.2.4 shall be 
scrupulously followed, and 

3) The earths and short-circuits, specified 
on the permit-to-work shall not be 
removed or interfered with except by 
authority from the person-in-charge of 
the work. 

4.2.2 Minimum Working Distance 

No person shall work within the minimum working 
distance from the exposed live mains and apparatus. 
The minimum working distance depends upon the 
actual voltages. It does not apply to operations carried 
out on mains and apparatus which are so constructed 
as to permit sale operation within these distances. 
Exposed live equipment in the vicinity shall be 
cordoned off so that persons working on the released 
equipment in service. The cordoning off shall be done 
in such a way that it does not hinder the movement of 



PART 1 GENERAL AND COMMON ASPECTS 



187 



SP 30 : 2011 



the maintenance personnel. If necessary, a safety 
sergeant could be posted. 

4.2.3 Isolation of Mains 

Isolation of mains shall be effected by the following 
methods: 

a) The electrical circuits shall be broken only by 
authorized persons by disconnecting switches, 
isolating links, unbolting connections or 
switches which are racked out. Where possible, 
the isolation should be visibly checked, and 

b) Where the means of isolation are provided 
with a device to prevent their reclosure by 
unauthorized persons, such a device shall be 
used. 

4.2.4 Devices for Proving Mains and Apparatus Dead 

4.2.4.1 High voltage neon lamp contact indicators rods 
are often used for proving exposed mains and apparatus 
dead. Each rod is fitted with an indicating neon tube 
or other means which glows when the contact end of 
the rod comes in contact with exposed live parts. Each 
rod is clearly marked for the maximum voltage on 
which it may be safely used and shall not, under any 
circumstances, be used on higher voltages. 

4.2.4.2 Contact indicator and phasing rods are provided 
for phasing and proving exposed mains and apparatus 
dead. A set consists of two rods connected in series by 
a length of insulated cables. Both rods are fitted with 
contact tips and indicating tubes. When the contact tip 
of one rod is applied to exposed live parts and that of 
the other earth or other exposed live parts provided 
there is sufficient voltage difference between the two, 
the indicating tubes should glow. Each set of rods is 
normally marked for the maximum voltage on which 
it may be used and shall not, under any circumstances, 
be used on higher voltages. 

4.2.4.3 Use of contact indicator and phasing rods 

While using the high voltage contact indicator and 
phasing rods for proving the mains or apparatus dead, 
following precautions should be taken: 

a) Ensure that the rod is clean and dry, 

b) Check the rod by applying it to known live 
parts of the correct voltage, the indicating tube 
shall glow, 

c) Apply the rod to each phase required to be 
proved dead, the indicating tube shall not 
glow. Be very careful to be in a position to 
see the glow, if any, appearing in the indicating 
tube, and 

d) Again check the rod by applying it to live parts 
as in 4.2.4.3 (b). Again the indicating tubes 
shall glow. 



NOTES 

1 All the above operations shall be carried out at the same place 
and at the same time, if no live parts are available on the site, 
rods up to 1 1 kV may be tested by applying them to the top of 
the spark plug in a running motor car engine. If the rod is in 
order the indicating tube will glow each time the plug sparks. 
Therefore, the glow will to intermittent, but the indicating tube 
should glow on this test or the rod is useless as a means of 
proving the mains or apparatus dead. 

2 The rod should be tested both before and after the use. 

4.2.4.4 Testing and marking of devices 

It shall be ensured that all devices for proving high 
voltage mains and apparatus dead are marked clearly 
with the maximum voltage for which they are intended 
and should be tested periodically. 

4.2.4.5 Identification of cables to be worked upon 

A cable shall be identified as that having been proved 
dead prior to cutting or carrying out any operation 
which may involve work on or movement of the cable. 
A non-contact indicating rod, induction testing set or 
spiking device may be used for proving the cable dead. 

4.2.4.6 Earthing and short-circuiting mains 

a) High voltage mains shall not be worked upon 
unless they are discharged to earth after 
making them dead and are earthed and short- 
circuited with earthing and short-circuiting 
equipment is adequate to carry possible short- 
circuit currents and specially meant for the 
purpose. All earthing switches wherever 
installed should be locked up. 

b) If a cable is required to be cut, steel wedge 
shall be carefully driven through it at the point 
where it is to be cut or preferably by means 
of a spiking gun of approved design. 

c) After testing the cable with dc voltage, the 
cable shall be discharged through a 2 megohm 
resistance and not directly, owing to dielectric 
absorption which is particularly prominent in 
the dc voltage testing of high voltage cables. 
The cable shall be discharged for a sufficiently 
long period to prevent rebuilding up of 
voltage. 

d) The earthing device when used shall be first 
connected to an effective earth. The other end 
of the device shall then be connected to the 
conductors to be earthed. 

e) Except for the purpose of testing, phasing, etc, 
the earthing and short-circuiting devices shall 
remain connected for the duration of the work. 

4.2.4.7 Removing the earth connections 

On completion of work, removal of the earthing and 
short-circuiting devices shall be carried out in the 
reverse order to that adopted for placing them 



188 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



(see 4.2A.6), that is, the end of the earthing device 
attached to the conductors of the earthed mains or 
apparatus shall be removed first and the other and 
connected to earths shall be removed last. The 
conductor shall not be touched after the earthing device 
has been removed from it. 

4.2.4.8 Safety precautions for earthing 

The precautions mentioned below should be adopted 
to the extent applicable and possible: 

a) Examine earthing devices periodically and 
always prior to their use, 

b) Use only earthing switches or any other 
special apparatus where provided for earthing, 

c) Verify that the circuit is dead by means of 
discharging rod or potential indicator. The 
indicator itself should first be tested on a live 
circuit before and after the verification, 

d) Earthing should be done in such a manner that 
the persons doing the job are protected by 
earth connections on both sides of their 
working zone, and 

e) All the three phases should be effectively 
earthed and short-circuited though work may 
be proceeding on one phase only. 

4.2.4.9 Working on mains where visible isolation 
cannot be carried out 

Where the electrical circuit cannot be broken visibly 
as set out in 4.23 the circuit may be broken by two 
circuit opening devices, one on each side of the work 
zone, where duplicate feed is available and by one 
circuit opening device where duplicate feed is not 
available provided the following conditions are fulfilled: 

a) The position of the contacts of the circuit 
opening device(s) — 'open' or 'closed' — is 
clearly indicated by the position of the 
operating handle or by signal lights or by other 
means. 

b) The circuit opening device(s) can be locked 
mechanically in the open position. 

c) The mains and apparatus to be worked on are 
adequately earthed and short-circuited 
between the circuit opening device and the 
position of the work. 

d) In cases where duplicate feed is available, 
both the circuit opening devices are in series 



between the mains and apparatus to be worked 
on and any source of supply, 
e) In cases where duplicate feed is not available, 
the circuit opening device is between the 
mains to be worked on and any source of 
supply. 

The circuit opening devices mentioned above shall be 
locked in the open position before the work on the 
mains and apparatus is commenced. The locking 
devices shall be removed only by a competent person 
and not until the work has been completed, any short- 
circuiting and earthing removed and the permit-to- work 
form duly returned and cancelled. 

4.2.4.10 Work on mains with two or more sections 

When the mains to be worked upon are to be divided 
into two or more sections, the provisions of 4.2.3, 
4.2.4.6 and 4.2.4.9 shall be observed with regard to 
each section. 

5 SAFETY PRACTICES 

5.1 In all electrical works, it is very necessary that 
certain elementary safety practices are observed. It has 
been found that quite a large number of accidents occur 
due to the neglect of these practices. The details of 
such practices are given in Annex C of IS 5216 (Part 1). 

5.2 Equipment, Devices and Appliances 

General guidelines on equipment, devices and 
appliances are given in IS 5216 (Part 1). 

6 SAFETY POSTERS 

6.1 The owner of every medium, high and extra high 
voltage installation is required to fix permanently, in a 
conspicuous position a danger notice in Hindi or 
English and the local language of the district on every 
motor, generator, transformer, all supports or high and 
extra high voltage etc. The danger notice plate shall 
conform to IS 2551. 

6.2 It is also recognized as good practice to indicate by 
means of the symbol recommended in IS 8923 on 
electrical equipment where the hazards arising out of 
dangerous voltage exist. 



7 ACCIDENTS AND 
ELECTRIC SHOCK 



TREATMENT FOR 



See SP 31 and IS 5216 (Part 2), 



PART 1 GENERAL AND COMMON ASPECTS 



189 



SP 30: 2011 



SECTION 20 TABLES 



FOREWORD 

In electrical engineering work, frequent need arises to 
make reference to certain data, which, when made 
available in the form of ready reference tables facilitates 
the work. Those tables which basically provide 
fundamental data not necessarily required for the 
understanding of the Code but are required to be 
referred to in designing the installation are given in 
this Section. 

1 SCOPE 

This Part 1 /Section 20 gives frequently referrred tables 
in electrical engineering work. 



2 REFERENCES 

The following Indian Standards may be referred for 
further details: 



IS No. 




Title 


3961 




Recommended current ratings for 
cables: 


(Part 1) : 


: 1967 


Paper insulated lead sheathed cables 


(Part 2) : 


: 1967 


PVC insulated and PVC sheathed 
heavy duty cables 


(Part 3) : 


1968 


Rubber insulated cables 


(Part 4) : 


: 1968 


Polyethylene insulated cables 


IS 11955: 


: 1987 


Preferred current ratings 



Table 1 Diameter and Maximum Allowable Resistance of Fuse- Wire, Tinned Copper 



SI No. 


Rated Current of 


Nominal Diameter 


Tolerance 


Permissible Resistance at 20°C 




Fuse-Wire 






Max 




Mm 




A 


mm 


mm 


Q/m 




ft/m 


(1) 


(2) 


(3) 


(4) 


(5) 




(6) 


i) 


6 


0.20 


±0.003 


0.564 4 




0.525 


ii) 


10 


0.35 


±0.004 


0.183 4 




0.173 


iii) 


16 


0.50 


± 0.005 


0.089 8 




0.084 8 


iv) 


20 


0.63 


±0.006 


0.056 6 




0.053 5 


v) 


25 


0.75 


±0.008 


0.040 




0.037 6 


vi) 


32 


0.85 


±0.009 


0.031 1 




0.029 3 


vii) 


40 


1.25 


±0.011 


0.014 3 




0.013 6 


viii) 


63 


1.50 


±0.015 


0.009 9 




0.009 4 


ix) 


80 


1.80 


±0.018 


0.006 9 




0.006 5 


x) 


100 


2.00 


±0.020 


0.005 6 




0.005 3 



Table 2 Size of Wood Casing and Capping, and Number of Cables that may be 
Drawn in One Groove of the Casing 



SI No. Width of Casing of Capping, mm 



38 



44 



51 



64 



76 



89 



102 



i) No. of grooves 

ii) Width of grooves, mm 

iii) Width of dividing fillet, mm 

iv) Thickness of outer wall, mm 

v) Thickness of casing, mm 

vi) Thickness of capping, mm 

vii) Thickness of the back under the groove, mm 

viii) Length, m 



2 


2 


2 


2 


2 


2 


2 


6 


6 


9 


13 


16 


16 


19 


a 


12 


13 


18 


24 


35 


38 


i 


10 


10 


10 


10 


11 


13 


[6 


16 


19 


19 


25 


32 


32 


6 


6 


10 


10 


10 


13 


13 


6 


6 


6 


10 
2.5 to 3.0 


10 


10 


13 



190 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



Table 2 — (Concluded) 



Size of Cable 




Number of Cables that 


may 


be Drawn in 


One Groove 




Nominal Cross- 
Sectional Area, mm 2 


Number and Diameter 
(in mm) of Wires 




1.0 


1/L12 ,} 


2 


2 


3 


3 


9 


12 


12 


1.5 


1/1.40 


1 


1 


2 


2 


8 


12 


12 


2.5 


1/1.80 
3/1 .60 n 


1 


1 


2 


2 


5 


10 


10 


4 


1/2.24 
7/1.85 1} 


— 


— 


2 


2 


5 


8 


9 


6 


1/2.80 
7/1.06 


— 


— 


1 


1 


4 


6 


6 


10 


l/3.55 2) 
7/1.40 


— 


— 


1 


1 


3 


5 


5 


16 


7/1.70 


— 


— 


— 


__ 


1 


2 


2 


25 


7/2.24 


— 


___ 


— 


— 


1 


1 


1 


35 


7/2.50 


— 


— 


— 


— 


1 


1 


1 


50 


7/3.00 2) 

■s only, 
ictors only. 










1 


1 


1 


°For copper conductoi 
2) For aluminium condi 





Table 3 Maximum Permissible Number of 1.1 kV Grade Cables that can be Drawn into 

Rigid Steel Conduits 



Size of Cable 



Size of Conduit, mm 



Nominal Number and 
Cross- Diameter 

Sectional Area (in mm) 
mm 2 of Wires 



16 



20 



25 



32 



40 



50 



Number of Cables, Max 



63 



(1) 



(2) 



S B S B S B S B S B S B S B 

(3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) 



1.0 
1.5 

2.5 



6 
10 

16 

25 
35 
60 



1/1.12° 

1/1.40 

1/1.80 

3/1.06 !) 

1/2.24 

7/0.85 ,} 
11/2.80 

7/0.6 S) 
ll/3.55 2) 

7/1. 40" 

7/1.70 

7/2.24 

7/2.50 
19/1.80 

7/3.007 2) 



2 — 



13 
12 
10 



10 
10 



20 
20 
18 

12 

10 

8 
6 

4 
3 

2 



14 
14 
12 

10 



6 9 7 

5 8 6 

4 9 5 



NOTE — The table shows the maximum capacity of conduits of the simultaneous drawing of cables, the table applies to 1.1 kV grade 
cables. The columns headed S apply to runs of conduit which have distance not exceeding 4.25 m between draw-in-boxes, and which 
do not deflect from the straight by an angle of more than 15°. The columns headed B apply to runs of conduit which deflect from the 
straight by an angle of more than 15°. 

]) For copper conductors only. 
a) For aluminium conductors only. 



PART 1 GENERAL AND COMMON ASPECTS 



191 



SP 30: 2011 

Table 4 Maximum Permissible Number of 1.1 kV Grade Single-Core Cables that may be Drawn into 

Rigid Non-metallic Conduits 



Size of Cable 






Size of Conduit, mm 






Nominal Cross- 
Sectional Area 


Number and 
Diameter of 


16 


20 


25 


32 


40 


50 


mm 2 


Wires, mm 






Number of Cables, Max 






(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


(7) 


(8) 


1.0 


1/1.12 1} 


5 


7 


13 


20 








1.5 


1/1.40 


4 


6 


10 


14 


— 





2.5 


1/1.80 
3/1.06 ]) 


3 


5 


10 


14 


— 





4 


1/2.24 
7/0.85 ,} 


2 


3 


6 


10 


14 





6 


1/2.80 
7/1. 40 u 


— 


2 


5 


9 


11 





10 


l/3.55 2) 
7/1.40 1) 


— 


— 


4 


7 


9 





16 


7/1.70 


— 


— 


2 


4 


5 


12 


25 


7/2.24 


— 


— 


— 


2 


2 


6 


35 


7/2.50 


— 


— 


— 


— 


2 


5 


50 


7/3.00 2} 
19/1.80 










2 


5 


n For copper 


conductors only. 




2) For aluminium conductors only. 















Table 5 Capacitor Sizes for Power Factor Improvement 



Existing 
Power 










Improved Poi 


^er Facte 
0.94 


>r 












Factor 


0.80 


0.85 


0.90 


0.91 


0.92 


0.93 


0.95 


0.96 


0.97 


0.98 


0.99 


1.00 


(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


(7) 


(8) 


(9) 


(10) 


(11) 


(12) 


(13) 


(14) 












Multiplying 


Factors 














0.40 


1.537 


1.668 


1.805 


1.832 


1.861 


1.895 


1.924 


1.959 


1.998 


2.037 


2.085 


2.146 


2.288 


0.41 


1.474 


1.605 


1.742 


1.769 


1.798 


1.831 


1.860 


1.896 


1.935 


1.973 


2.021 


2.082 


2.225 


0.42 


1.41.3 


1.544 


1.681 


1.709 


1.738 


1.771 


1.800 


1.836 


1.874 


1.913 


1.961 


2.022 


2.164 


0.43 


1.356 


1.487 


1.624 


1.651 


1.680 


1.713 


1.742 


1.778 


1.816 


1.855 


1.903 


1.964 


2.107 


0.44 


1.290 


1.421 


1.558 


1.585 


1.614 


1.647 


1.677 


1.712 


1.751 


1.790 


1.837 


1.899 


2.041 


0.45 


1.230 


1.360 


1.501 


1.532 


1.561 


1.592 


1.626 


1.659 


1.695 


1.737 


1.784 


1.846 


1.988 


0.46 


1.179 


1.309 


1.446 


1.473 


1.502 


1.533 


1.567 


1.600 


1.636 


1.677 


1.725 


1.786 


1.929 


0.47 


1.130 


1.260 


1.397 


1.425 


1.454 


1.485 


1.519 


1.552 


1.588 


1.629 


1.677 


1.758 


1.881 


0.48 


1.076 


1.206 


1.343 


1.370 


1.400 


1.430 


1.464 


1.497 


1.534 


1.575 


1.623 


1.684 


1.826 


0.49 


1.030 


1.160 


1.297 


1.326 


1.355 


1.386 


1 .420 


1.453 


1.489 


1.530 


1.578 


1.639 


1.782 


0.50 


0.982 


1.112 


1.248 


.276 


1.303 


1.337 


1.369 


1.403 


1.441 


1.481 


1.529 


1.590 


1.732 


0.51 


0.936 


1.066 


1.202 


1.230 


1.257 


1.291 


1.323 


1.357 


1.395 


1.435 


1.483 


1.544 


1.686 


0.52 


0.894 


1.024 


1.160 


1.188 


1.215 


1.149 


1.281 


1.315 


1.353 


1.393 


1.441 


1.502 


1.644 


0.53 


0.850 


0.980 


1.116 


1.144 


1.171 


1.205 


1.237 


1.271 


1.309 


1.349 


1.397 


1.458 


1.600 


0.54 


0.809 


0.939 


1.075 


1.103 


1.130 


1.164 


1.196 


1.230 


1.268 


1.308 


1.356 


1.417 


1.559 


0.55 


0.769 


0.899 


1.035 


1.063 


1.090 


1.124 


1.136 


1.190 


1.228 


1.268 


1.316 


1.377 


1.519 


0.56 


0.730 


0.860 


0.996 


1.024 


1.051 


1.085 


1.117 


1.151 


1.189 


1.229 


1.277 


1.338 


1.480 


0.57 


0.692 


0.822 


0.958 


0.986 


1.013 


1.047 


1.079 


1.113 


1.151 


1.191 


1.239 


1.300 


1.442 


0.58 


0.655 


0.785 


0.921 


0.949 


0.976 


1.010 


1.042 


1.076 


1.114 


1.154 


1.202 


1.263 


1.405 


0.59 


0.618 


0.748 


0.884 


0.912 


0.939 


0.973 


1.005 


1.039 


1.077 


1.117 


1.165 


1.226 


1.368 


0.60 


0.584 


0.714 


0.849 


0.878 


0.905 


0,939 


0.971 


1.005 


1.043 


1.083 


1.131 


1.192 


1.334 


0.61 


0.549 


0.679 


0.815 


0.843 


0.870 


0.904 


0.936 


0.970 


1.008 


1.048 


1.096 


1.157 


1.299 



192 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 













Table 5 — (Concluded) 












Existinj 


j 








Improved Power Factor 












Power 
Factor 




























0.80 


0.85 


0.90 


0.91 


0.92 


0.93 


0.94 


0.95 


0.96 


0.97 


0.98 


0.99 


1.00 


(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


(7) 


(8) 


(9) 


(10) 


(11) 


(12) 


(13) 


(14) 


0.62 


0.515 


0.645 


0.781 


0.809 


0.836 


0.870 


0.902 


0.936 


0.974 


1.014 


1.062 


1.123 


1.265 


0.63 


0.483 


0.613 


0.749 


0.777 


0.804 


0.838 


0.870 


0.902 


0.942 


0.982 


1.030 


1.091 


1.233 


0.64 


0.450 


0.580 


0.716 


0.744 


0.771 


0.805 


0.837 


0.871 


0.909 


0.949 


0.997 


1.058 


1.200 


0.65 


0.419 


0.549 


0.685 


0.713 


0.740 


0.774 


0.806 


0.840 


0.878 


0.918 


0.966 


1.027 


1.169 


0.66 


0.388 


0.518 


0.654 


0.682 


0.709 


0.743 


0.775 


0.809 


0.847 


0.887 


0.935 


0.996 


1.138 


0.67 


0.358 


0.488 


0.624 


0.652 


0.679 


0.713 


0.745 


0.779 


0.817 


0.857 


0.905 


0.966 


1.108 


0.68 


0.329 


0.459 


0.595 


0.623 


0.650 


0.684 


0.716 


0.750 


0.788 


0.828 


0.876 


0.937 


1.079 


0.69 


0.299 


0.429 


0.565 


0.593 


0.620 


0.654 


0.686 


0.720 


0.758 


0.798 


0.840 


0.907 


1.049 


0.70 


0.270 


0.400 


0.536 


0.564 


0.591 


0.625 


0.657 


0.691 


0.729 


0.769 


0.811 


0.878 


1.020 


0.71 


0.242 


0.372 


0.508 


0.536 


0.563 


0.597 


0.629 


0.663 


0.701 


0.741 


0.785 


0.850 


0.992 


0.72 


0.213 


0.343 


0.479 


0.507 


0.534 


0.568 


0.600 


0.634 


0.672 


0.712 


0.754 


0.821 


0.963 


0.73 


0.186 


0.316 


0.452 


0.480 


0.507 


0.541 


0.573 


0.607 


0.648 


0.685 


0.727 


0.794 


0.936 


0.74 


0.159 


0.289 


0.425 


0.453 


0.480 


0.514 


0.546 


0.580 


0.618 


0.658 


0.700 


0.740 


0.909 


0.75 


0.132 


0.262 


0.398 


0.426 


0.453 


0.487 


0.519 


0.553 


0.591 


0.631 


0.673 


0.713 


0.882 


0.76 


0.105 


0.235 


0.371 


0.399 


0.426 


0.460 


0.492 


0.526 


0.564 


0.604 


0.652 


0.687 


0.855 


0.77 


0.079 


0.209 


0.345 


0.373 


0.400 


0.434 


0.466 


0.500 


0.538 


0.578 


0.620 


0.661 


0.829 


0.78 


0.053 


0.183 


0.319 


0.347 


0.374 


0.408 


0.440 


0.474 


0.512 


0.552 


0.592 


0.634 


0.803 


0.79 


0.026 


0.156 


0.292 


0.320 


0.347 


0.381 


0.413 


0.447 


0.485 


0.525 


0.567 


0.608 


0.776 


0.80 


__ 


0.130 


0.266 


2.294 


0.321 


0.355 


0.387 


0.421 


0.459 


0.499 


0.541 


0.582 


0.750 


0.81 


— 


0.104 


0.240 


0.268 


0.295 


0.329 


0.361 


0.395 


0.433 


0.473 


0.515 


0.556 


0.724 


0.82 


— 


0.078 


0.214 


0.242 


0.269 


0.303 


0.335 


0.369 


0.407 


0.447 


0.489 


0.530 


0.698 


0.83 


— 


0.052 


0.188 


0.216 


0.243 


0.277 


0.309 


0.343 


0.381 


0.421 


0.463 


0.504 


0.672 


0.84 


— 


0.026 


0.162 


0.190 


0.217 


0.251 


0.283 


0.317 


0.355 


0.395 


0.417 


0.450 


0.620 


0.85 


— 


— 


0.136 


0.164 


0.191 


0.225 


0.257 


0.291 


0.329 


0.369 


0.417 


0.450 


0.620 


0.86 


_. 


— 


0.109 


0.140 


0.167 


0.198 


0.230 


0.264 


0.301 


0.343 


0.390 


0.424 


0.593 


0.87 


— 


— 


0.083 


0.114 


0.141 


0.172 


0.204 


0.238 


0.275 


0.317 


0.364 


0.395 


0.567 


0.88 


— 


_ 


0.054 


0.085 


0.112 


0.143 


0.175 


0.209 


0.246 


0.288 


0.309 


0.369 


0.512 


0.89 


___ 


— 


0.028 


0.059 


0.086 


0.117 


0.149 


0.183 


0.230 


0.262 


0.309 


0.369 


0.512 


0.90 


— 


— 


— 


0.031 


0.058 


0.089 


0.121 


0.155 


0.192 


0.234 


0.281 


0.341 


0.484 


0.91 


— 


___ 


__ 


— 


0.027 


0.058 


0.090 


0.124 


0.161 


0.203 


0.250 


0.310 


0.453 


0.92 


— 


— 


__ 


_ 


— 


0.027 


0.063 


0.097 


0.134 


0.176 


0.223 


0.283 


0.426 


0.93 


— 


— 


— 


_ 


— 


— 


0.032 


0.066 


0.103 


0.145 


0.192 


0.252 


0.395 


0.94 


— 


_ 


— 


— 


— 


_ 


— 


0.034 


0.071 


0.113 


0.160 


0.220 


0.363 


0.95 


— 


— 


— 


— 


— 


— 


— 


— 


0.037 


0.079 


0.126 


0.186 


0.329 


0.96 


— 


— 


— 


— 


_ 


— 


— 


— 


— 


0.042 


0.089 


0.149 


0.292 


0.97 


— 


_ 


— 


— 


___ 


— 


— 


— 


— 


— 


0.047 


0.107 


0.250 


0.98 


— 


— 


— 


— 


— 


__„ 


— 


— 


__ 


— 


__ 


0.060 


0.203 


0.99 


— 


— 


— 


— 


— 


— 


— 


— 


— 


— 


_ 


— 


0.143 



NOTE — The consumer is advised to make proper allowance for lower supply voltages where these exist during the working hours 
and may choose slightly higher kVAR than recommended in the table for such cases. 



PART 1 GENERAL AND COMMON ASPECTS 



193 



NATIONAL ELECTRICAL CODE 

PART 2 



SP 30 : 2011 



PART 2 ELECTRICAL INSTALLATIONS IN 

STAND-BY GENERATING STATIONS AND 

CAPTIVE SUBSTATIONS 

FOREWORD 

This National Electrical Code (Part 2) is primarily intended to cover the requirements relating to stand-by generating 
stations and captive substations intended for serving an individual occupancy. As the general provisions relating 
to such installations are common and are themselves elaborate in nature, it was felt essential to cover them in a 
separate part preceding the other parts which cover the requirements for specific installations. 

Generating stations covered by this Part 2 are the stand-by or emergency supply and captive substations normally 
housed in or around the building in question. This Code does not include the switching stations and other large 
generating plants coming solely under the preview of the electric supply authority of a metropolis even though to 
some extent the requirements stipulated herein could also be applicable to them. 

Specific requirements if any, for generating and switching substations for individual buildings that might vary 
depending on the nature of the occupancy or the size of the building are enumerated in the respective sections of 
the Code. 

In the formulation of this Code, note has been taken of the requirements stipulated in installation Codes of 
individual equipment as well as the fire- safety Codes for generating stations and substations. It is generally not 
feasible to draw very strict guidelines for the design and layout for such installations owing to the complexity of 
the needs of building installations and hence only the essential safety considerations are listed out for compliance. 
It is essential to take recourse to the assistance of local authorities for further details. 

Specific requirements pertaining to stand-by generating stations and captive substations for multistoreyed/high- 
rise buildings are covered in Part 3/Section 7 of this Code. 

PART 2 ELECTRICAL INSTALLATIONS IN STAND-BY GENERATING STATIONS AND CAPTIVE SUBSTATIONS 197 



SP 30: 2011 



1 SCOPE 

1.1 This Code (Part 2) covers essential requirements 
for electrical installations in stand-by generating 
stations and captive substations intended to serve a 
building or group of buildings. 

1.2 This Part is not intended to cover 'captive generator 
sets' of very large capacities. This Part 2 covers only 
the stand-by generating sets upto the capacity of 5 MW. 
Similarly the substations upto the capacities of 10 MVA 
and 33 kV are covered. This Part 2 also does not apply 
to the generating stations coming under the jurisdiction 
of the Electric Supply Authority in a city or metropolis. 

2 REFERENCES 

This Part 2 should be read in conjunction with the 
following Indian Standards: 



IS No. 
1641 : 1988 



1642 : 1989 



1646 : 1997 



1946 : 1961 



2309 : 1989 



3034 : 1993 



3043 : 1987 

10028 (Part 2) : 
1981 

10118 (Part 3): 
1982 



Title 

Code of practice for fire-safety of 
buildings (general): General 
principles of fire grading and 
classification 

Code of practice for fire safety of 
buildings (general): Details of 
construction (first revision) 
Code of practice for fire-safety of 
buildings (general): Electrical 
installation (second revision) 
Code of practice for use of fixing 
devices in walls, ceilings and of 
solid construction 
Code of practice for the protection 
of buildings and allied structures 
against lightning (second revision). 
Fire-safety of industrial buildings: 
Electrical generating and 
distributing stations — Code of 
practice (second revision) 
Code of practice for earthing (first 
revision) 

Code of practice for selection, 
installation and maintenance of 
transformers: Part 2 Installations 
Code of practice for selection, 
installation and maintenance of 
switchgear: Part 3 Installation 



3 TERMINOLOGY 

For the purpose of this Part, the definitions given in 
Part 1/Section 2 of this Code shall apply. 

4 GENERAL CHARACTERISTICS OF STATION 
INSTALLATIONS 

4.1 In determining the general characteristics of 



stand-by generating plants and building substations in 
a building, the assessment of characteristics of the 
buildings based on its occupancy shall be taken note 
of as specified in individual Parts/Sections of this Code. 

4.2 Depending on the exact location of the station in 
the building premises, and depending on whether the 
equipment are installed indoor or outdoor, the degree 
of external influence of the environment shall 
be determined based on the guidelines given in 
Part 1/Section 8 of this Code. 

4.3 It is generally presumed that generating stations 
and substations are restricted areas not meant for 
unauthorized persons, and such electrical operating 
areas fall under the category of BA4 utilization for 
instructed personnel (see Part 1/Section 8), which are 
adequately advised or supervised by skilled persons 
to avoid dangers that may arise owing to the use of 
electricity. 

5 EXCHANGE OF INFORMATION 

5.1 Information shall be exchanged amongst the 
personnel involved regarding the size and nature of 
substation and supply station requirements to be 
provided for an occupancy so that the type of 
equipment and their choice, as well as their installation 
shall be governed by the same. An assessment shall 
also be made of the civil construction needs of the 
station equipment keeping in view a possible expansion 
in future. 

5.2 Before ordering the equipment, information shall 
be exchanged, regarding the installation and location 
conditions, including such building features as access 
doors, lifting beams, oil pumps, cable trenches, 
foundation details for heavy equipment, ventilating 
arrangement, etc. 

6 LAYOUT AND BUILDING CONSTRUCTION 
ASPECTS 

6.1 The constructional features of all building housing 
the station installation shall comply with IS 1641, 
IS 1642 and IS 3034. Locating of substation in lowest 
basement is not recommended. 

6.2 Switchgears, circuit-breaker and transformers 
(except outdoor types) shall be housed preferably in 
detached single storey buildings of Type 1 construction. 
In the case of built up areas in cities, multistoreyed 
construction may also be adopted. Construction of such 
buildings shall conform to IS 1946. 

6.3 Construction of fire separation walls shall conform 
with the requirements of relevant Indian Standards. 
Doorway openings in separating walls of transformer 
or switchgear rooms shall be provided with sills not 
less than 15 cm in height. Reference is drawn to 



198 



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IS 3034, Where risk of spread of possible fire exists, 
interconnecting doors should have a 2 h fire rating. 

6.4 The foundation of the stand-by generating sets shall 
preferably be isolated from that of the other structures 
of the building so that vibrations are not carried over. 

6.5 The diesel generating (DG) set should be provided 
with integral acoustic enclosure conforming to the 
requirements as laid down in Environment Protection 
Act 

7 SELECTION OF EQUIPMENT 

7.1 The selection of equipment shall be done in 
accordance with the guidelines provided in Part 1/ 
Section 9 of this Code. 

8 GENERATING SETS 

8.0 Stationary generating sets of 5 kVA and above are 
normally driven by diesel engine as this drive is most 
economical. Smaller sets are driven by petrol. During 
the planning of the building, the dimensions of the 
power plant room and the transport ways shall be agreed 
to between the architect and electrical contractor. 

8.1 In case of large capacity sets which generate 
appreciable heat, the rooms shall be well ventilated 
and provided with air exhaust equipment. 

8.2 The capacity of the stand-by set for an installation 
should be such that in an event of power failure, the 
essential loads can be supplied power. For instance in 
case of hospitals such loads comprise operation theatres 
and their supporting auxiliaries; intensive care units, 
cold storage in laboratories, emergency lifts, etc. In 
the case of industries having continuous processes, 
such loads are required to be supplied with power all 
the time. In commercial premises and high-rise 
buildings, a few lifts and circulation area lights and 
fire-fighting equipment have to be kept working by 
supply from stand-by sets. Similar is the case of 
essential loads in large hotels. Such sets can either be 
manually started and switched on to essential loads 
with the use of changeover switches or they could be 
auto-start on mains failure and loads autochanged over 
to generator supply. 

8.3 In case of large electrical installation in which 
essential loads are widely scattered it becomes 
necessary to run the generating set supply cables to 
these essential loads and in the event of mains failure, 
changeover to generator supply, either manually or 
through auto-changeover connectors, 

8.4 The fire safety requirements for fuel oil storage 
shall conform to 5.3 of IS 3034. 

8.5 The fire safety requirements for oil and gas fired 
installations shall conform to IS 3034. 



8.6 All equipment of prime mover shall conform to 
relevant Indian Standard (where they exist) for 
construction, temperature-rise, overload and 
performance. 

8.7 The diesel generator set should meet the pollution 
norms of the Central and State Statutory Authorities. 

9 TRANSFORMER INSTALLATIONS 

9.1 Reference is drawn to the requirements given in 
IS 10028 (Part 2). 

9.2 Transformer of capacity up to 3 MVA may be 
housed indoor or outdoor. The larger ones, because of 
their size, are usually of outdoor type. 

9.3 Indoor transformer will require adequate ventilation 
to take away as much heat as possible. Oil drainage 
facilities and partition walls between transformers and 
between transformer and other equipment such as oil 
circuit-breakers are necessary to reduce the risk of 
spread of fire. 

9.4 As a transformer station normally has a high voltage 
and a low voltage switchgear, all such equipment 
should be adequately separated. 

9.5 Only dry type transformer(s) shall be used for 
installation inside the residential/commercial buildings. 
The transformer room should be located on ground 
floor inside a well ventilated room. 

10 HIGH VOLTAGE SWITCHING STATIONS 

Reference is drawn to the requirements stipulated in 
IS 101 18 (Part 3). 

11 LOW VOLTAGE SWITCHING STATIONS 
AND DISTRIBUTION PANELS 

Reference is drawn to the requirements stipulated in 
IS 10118 (Part 3). 

12 STATION AUXILIARIES 

12.0 Station auxiliaries could consist of: 

a) batteries for stand-by generating sets, 

b) batteries for short time emergency lighting, 

c) battery charging equipment, 

d) fuel oil pumps, 

e) ventilating equipment, and 

f) fire-fighting equipment. 

12.1 Batteries 

12.1.1 Batteries shall have containers of glass or any 
other non-corrosive, non-flammable materials. 

12.1.2 Batteries shall be installed in a separate 
enclosure away from any other auxiliary equipment or 
switchgear. The enclosure shall be free from dust and 



PART 2 ELECTRICAL INSTALLATIONS IN STAND-BY GENERATING STATIONS AND CAPTIVE SUBSTATIONS 



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well ventilated. Care shall be taken to ensure that direct 
sunlight does not fall on the batteries. 

NOTE — Provision shall be made for sufficient diffusion and 
ventilation of gases from the battery to prevent the 
accumulation of an explosive mixture. 

12.1.3 The batteries shall stand directly on durable, non- 
ignitable, non-absorbent and non-conducting material, 
such as glass, porcelain or glazed earthenware. These 
materials shall rest on a bench which shall be kept dry 
and insulated from earth. If constructed of wood it shall 
be slatted and treated with anti-sulphuric enamel. 

12.1.4 The batteries shall be so arranged on the bench 
that a potential difference exceeding 12 V shall not 
exist between adjoining cells. The batteries not 
exceeding 20V shall not be bunched or arranged in 
circular formation. 

12.1.5 All combustible materials within a distance 
of 60 cm measured horizontally from, or within 2.0 m 
measured vertically above, any battery shall be 
protected with hard asbestos sheets. 

12.2 Battery Charging Equipment 

12.2.1 The battery charging equipment with necessary 
switch and controlgear shall be mounted separately and 
away from the batteries. 

12.3 Fuel Oil Pump 

12.3.1 Fuel oil pump shall be installed close to the 
engine room or inside the engine room. 

12.3.2 The electric cable provided to run the pump 
motor shall be protected with oil-resistant outer sheath. 

12.4 Ventilating Equipment 

12.4.1 The engine room shall be fitted with hot-air 
extractors. 

12.4.2 The battery room shall be fitted with exhaust 
fans. The exhaust gases be let off to atmosphere where 
no other equipment is installed. 

13 WIRING IN STATION PREMISES 

All cabling and electrical wiring inside generation or 
substation premises shall be done in accordance with 
the practice recommended in (Part 1/Section 9) of this 
Code. 

14 EARTHING 

The provision of 17 of IS 3043 shall apply (see also 
Part 1/Section 14). 



IS BUILDING SERVICES 

15.1 Lighting 

15.1.1 The general principal of good lighting for any 
occupancy shall be as given in Part 1/Section 11 of 
this Code. For the purpose of station installations the 
values of lumen level and limiting value of glare index 
shall be as given in Table 1 . 

Table 1 Recommended Values of Illumination 
and Glare Index 



No. 




Location 


Illumi- 
nation, 

lux 


Laminating 
Glare 
Index 


(1) 




(2) 


(3) 


(4) 


i) 


Indoor Locations 








a) 


Stand-by generator hall 


300 


25 




b) 


Auxiliary equipment; 
battery room, blowers, 
switchgear 




25 




c) 


Basements 


100 


25 




d) 


Control rooms: 










1) Vertical control panels 


300 


19 






2) Control desks 


300 


19 






3) Rear of control panel 


150 


19 


ii) 


Outdoor Locations 








a) 
b) 


Fuel oil storage area 
Transformers, outdoor 
switchgear 


50 
50 


19 
19 



15.2 The luminaires used shall be of dust-proof 
construction and shall be energy efficient with compact 
fluorescent lamps (CFL)/fluorescent lamps with 
electronic ballasts. 

16 FIRE-SAFETY REQUIREMENTS 

16.1 The provisions of IS 3034 and IS 1646 shall apply 
for station installations. 

16.2 All wiring for automatic fire-fighting installation 
shall be of fire-resistant outer sheath. 

17 LIGHTNING PROTECTION 
The provisions of IS 2309 shall apply. 

18 TESTING AND INSPECTION 

The guidelines provided in Part 1/Section 13 of this 
Code shall apply. In the case of diesel sets which come 
into operation only in emergency as stand-by sets, it is 
necessary that such sets are regularly checked run up 
and mechanical and electrical system tested to ensure 
that the set is in operable conditions all the time. 



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NATIONAL ELECTRICAL CODE 

PART 3 



SP 30: 2011 



PART 3. ELECTRICAL INSTALLATIONS IN 
NON-INDUSTRIAL BUILDINGS 



FOREWORD 

For the purposes of this Code, electrical installations 
in buildings have been broadly classified as those in 
non-industrial and industrial . While a majority of 
installations could be categorically classified as non- 
industrial, an industrial complex would necessarily 
incorporate sub-units such as offices, residential 
quarters and support services which are either housed 
or fall in the category of non-industrial buildings. The 
requirement stipulated in Part 3 and Part 4 of this Code 
would therefore require judicious application. 

With the current trend in power utilization, it would 
also be extremely difficult to classify electrical 
installations based on power requirement or the 
voltage of supply, as large buildings for non-industrial 
purposes consume sufficient power to consider them 
at par with the consumption of light industrial 
establishments. It is therefore necessary to consider 
for initial assessment of the installation the guidelines 
given in Part 1/Sec 8 this Code, which are better 
defined than the earlier terminology used for 
classifying installations. 

Part 3 of this Code, therefore covers requirements 



for major types of non-industrial occupations. It is 
felt that a large number of occupancies would fall 
in one of the categories, and for typical buildings 
which do strictly fall into any of these, recourse shall 
be made to the general guidelines stipulated in 
Parti. 

This Part consists of the following Sections: 

Section 1 Domestic Dwellings 

Section 2 Office Building, Shopping and 

Commercial Centres and Institutions 
Section 3 Recreational, Assembly Building 
Section 4 Medical Establishments 
Section 5 Hotels 
Section 6 Sports Buildings 
Section 7 Specific Requirements for Electrical 

Installations in Multistoried Buildings 

Sections 1-6 of this Part cover requirements applicable 
to buildings which are of nominal heights less than 
15 m. It is recognized that from the point of view fire- 
safety of buildings more than 15 m height require 
specific considerations. These are summarized in 
Section 7 of this Part. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



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SECTION 1 DOMESTIC DWELLINGS 



FOREWORD 

Electrical installations in domestic dwellings and in 
buildings providing living accommodation for people 
are by far the simplest form of installation. Use of 
electrical appliances, both portable and fixed has now 
become very common and popular even in single 
family dwellings. The optimum benefits from the use 
of electricity can be obtained only if the installation 
is of sufficient capacity and affords enough 
flexibility. 

The primary considerations in planning the electrical 
layout in domestic dwellings are economy and safety. 
Besides these, other considerations such as efficiency 
and reliability, convenience and provisions for future 
expansion are also valid. 

Domestic installations are characterized mainly by a 
circuit voltage of 250 V to earth except in the case of 
large power consumers where three-phase supply is 
given. A brief description of the type of installations 
covered in this Section is given in 4. It may, however, 
be noted that lodging and rooming houses, though 
utilized as living accommodation for short periods of 
time (by different occupants) are covered under scope 
of Part 3/Section 5 of this Code. 

Specific requirements for installations in rooms 
containing a bath tub or shower basin, namely, 
bathrooms are separately covered in Annex A. These 
requirements also apply to similar locations in other 
occupancies, such as hotels. For convenience, these 
requirements are covered in this Section. 

1 SCOPE 

This Part 3/Section 1 of the Code covers requirements 
for electrical installations in domestic dwellings. 

2 REFERENCES 

This Part 3/Section 1 of the Code should be read in 
conjunction with the following Indian Standards: 

IS No. Title 

3646 (Part 2) : 1966 Code of practice for interior 
illumination: Part 2 Schedule for 
values of illumination and glare 
index 

7689 : 1989 Guide for the control of 

undesirable static electricity 

8061 : 1976 Code of practice for design, 

installation and maintenance of 
service lines upto and including 
650 V 



IS No. 

13450 (Parti): 

1994 /IEC 

60601-1 : 1988 
14665(Part 1) : 
2000 



15707 : 2006 



SP7.-2005 
SP 72: 2010 



Title 

Medical electrical equipment — 
Part 1: General requirements for 
safety 

Electric traction lifts — Part 1: 
Guidelines for outline dimensions 
of passenger, goods, service and 
hospital lifts 

Testing, evaluation, installation 
and maintenance of ac electricity 
meters — Code of practice 
National Building Code of India 
National Lighting Code 



3 TERMINOLOGY 

For the purpose of this Section, the definitions given 
in Part 1/Section 2 of this Code shall apply. 

4 CLASSIFICATION 

4.1 The electrical installations covered in this Section, 
are those in buildings intended for the following 
purposes: 

4.1.1 Domestic Dwellings/ Residential Buildings 

These shall include buildings in which sleeping 
accommodation is provided for normal residential 
(domestic) purposes with cooking and dining facilities. 

Such buildings shall be further classified as follows: 

a) One or two family dwellings — These shall 
include any private dwelling which is 
occupied by members of a single family and 
has a total sleeping accommodation for not 
more than 20 persons. 

b) Apartment houses (flats) — These shall include 
any building or structure in which living quarters 
are provided for three or more families, living 
independently of each other and with 
independent cooking facilities. For example 
apartment houses, mansions and chawls. 

NOTE — If accommodation is provided for more than 
20 persons, such buildings are considered lodging or 
rooming houses, (dormitories) and the provisions of 
Part 3/Section 5 shall apply. 



5 GENERAL CHARACTERISTICS 
INSTALLATIONS 



OF 



General guidelines on the assessment of characteristics 
of installations in buildings are given in Part 1/Sec 8 
of this Code. For the purposes of installations falling 
under the scope of this Section, the characteristics 
defined below specifically apply. 



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5.1 Environment 

The following environmental factors shall apply to 
electrical installations in domestic dwellings: 



Environment 


Characteristics 


Remarks 


(1) 


(2) 


(3) 


Presence of 


Probability of 





water 


presence of water 
is negligible 




Presence of 


The quantity or 





foreign solid 


nature of dust or 




bodies 


foreign solid 
bodies is not 
significant 




Presence of 


The quantity and 


Applicable for 


corrosive or 


nature of 


most of the 


polluting 


corrosive or 


locations except 


substances 


polluting 


for dwellings 




substances is not 


situated by sea or 




significant 


in industrial zone 
in which case 
categorization AF2 
applies (see Part 
1/Sec 8) 


Mechanical 


Impact and 


Household and 


stresses 


vibration of low 
severity 


similar conditions 


Seismic effect 




Depends on the 


and lighting 




location of the 
building 



5.2 Utilization 

The following aspects utilization shall apply: 



Utilization 


Characteristics 


Remarks 


(1) 


(2) 


(3) 


Capability of 


Uninstructed 


Applies to all 


persons 


persons 


domestic 
installations 


Contact of 


Persons in 




persons 


normally 

conducting 

situations 




Conditions of 


Low density 


Buildings of 


evacuation 


occupation, easy 


normal or low 


during 


conditions of 


height used for 


emergency 


evacuation 


one or two 
family dwellings 




Low density 


Apartment 




occupation, 


houses including 




difficult 


high-rise flats 




conditions of 






evacuation 




Nature of 


No significant 




processed of 


risks 




stored material 







6 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

6.0 Exchange of Information 

6.0.1 Genera] aspects to be taken note of before 
designing the electrical installations are enumerated 
in Part 1/Section 7 of this Code. However, the 
following points shall be noted particularly in respect 
of domestic dwellings. 

6.0.2 Before starting wiring and installation of fittings 
and accessories, information should be exchanged 
between the owner of the building or architect or 
electrical contractor and the local supply authority in 
respect of tariffs applicable, types of apparatus that 
may be connected under each tariff, requirement of 
space for installing meters, switches, service lines, Qtc, 
and for total load requirement of lights, fans and power. 

6.0.3 While planning an installation, consideration 
should be given to the anticipated increase in the use 
of electricity for lighting, general purpose socket- 
outlet, kitchen, heating, etc. It is essential that adequate 
provision should be made for all the services which 
may be required immediately and during the intended 
useful life of the building, for the householder may 
otherwise be tempted to carry out extension of the 
installation himself or to rely upon use of multiplug 
adaptors and long flexible cords, both of which are 
not recommended. A fundamentally safe installation 
may be rendered dangerous, if extended in this way. 

6.0.4 Electrical installation in a new building should 
normally begin immediately on the completion of the 
main structural building work. For conduit wiring 
system, the work should start before finishing work 
like plastering has begun. For surface wiring system, 
however, work should begin before final finishing work 
like white washing, painting, etc. Usually, no 
installation work should start until the building is 
reasonably weatherproof, but where electric wiring is 
to be concealed within the structures, the necessary 
conduits and ducts should be positioned after the 
shuttering is in place and before the concrete is poured, 
provision being made to protect conduits from damage. 
For this purpose, sufficient coordination shall be 
ensured amongst the concerned parties. 

6.1.1 Estimation of Load Requirements 

The extent and form of electrical installations in 
domestic dwellings is basically designed to cater to 
light and fan loads and for electrical appliances and 
gadgets. In estimating the current to be carried by any 
branch circuit unless the actual values are known, these 
shall be calculated based on the following 
recommended ratings: 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



205 



SP 30: 2011 






Table 2 Recommended Schedule of J 




SI Item 




Recommended 


Docket-Outlets 


No. 




Rating 

(W) 
(3) 




(Clause 


6.1.3) 




(1) (2) 


SI No. 


Description 


Number of Socket- Outlets 


i) Incandescent lamps 




60 






6A 


16A 


ii) Ceiling fans 




60 


(1) 


(2) 


(3) 


(4) 


















i) 


Bedroom 


2-3 


1 


iii) Table fans 




60 
















ii) 


Living room 


2-3 


2 


iv) 6A, socket-outlet point unless 


100 


iii) 


Kitchen 


1 


2 


the actual value of loads 


are 












specified 






IV) 


Dining room 


2 


1 








v) 


Garage 


1 


1 


v) Fluorescent tubes: 






vi) 


For refrigerator 




1 


Length 600 mm 




25 














vii) 


For air-conditioner 


— 


1 (for each) 


1 200 mm 




50 


viii) 


Verandah 


1 per 10 m 2 


1 


1 500 mm 


>A) 


90 
1000 


ix) 


Bathroom 


1 


1 


vi) Power socket outlet (1( 










unless the actual value 


of 












loads are specified 






6.1.6 Balancing of circuits in three-wire or polyphase 
installation shall he nlanneH beforehand Tn p.anh rase 



6.1.2 Number of Points in Branch Circuits 

The recommended yardstick for dwelling units for 
determining the number of points is given in Table 1. 

Table 1 Number of Points for Dwelling Units 



SI Description 


Area for the Main Dwelling Unit (m 2 ) 


No. 


*~ 






'-N 




35 


45 


55 85 


140 


(1) (2) 


(3) 


(4) 


(5) (6) 


(7) 


i) Light points 


7 


8 


10 12 


17 


ii) Ceiling fans 


2-2 


3-2 


4-3 5-4 


7-5 


iii) 6 A Socket outlets 


2 


3 


4 5 


7 


iv) 16A Socket outlets 


— 


1 


2 3 


4 


v) Call-bell (buzzer) 


— 


— 


1 1 


1 


NOTE — The figures in table 


against 


SI No. (ii) indicate the 


recommended number of points and the number of fans. 




Example — For main dwelling 


I unit of 55 m 2 , 4 points 


with 3 


fans are recommended. 









6.1.3 Number of Socket-Outlets 

The recommended schedule of socket-outlets for the 
various sub-units of a domestic are given in Table 2. 

6.1.4 Selection of Size of Conductors 

Provisions of Part 1/Section 9 of this Code shall apply. 

6.1.5 'Power' sub-circuits shall be kept separate and 
distinct from 'lighting-and fan' sub-circuit. All wiring 
shall be done on the distribution system with main and 
branch distribution boards located at convenient 
physical and electrical load centres. All types of wiring, 
whether recessed or surface should be capable of easy 
inspection. The surface wiring when run along the walls 
should be as near the ceiling as possible. In all types 
of wirings due consideration shall be given for neatness 
and good appearance and safety. 



it is recommended that all socket-outlets in a room are 
connected to one phase. The conductors shall be so 
enclosed in earthed metal or incombustible insulating 
material that it is not possible to have ready access to 
them. If the points between which a voltage exceeding 
250 V is present are 2 m or more apart, the covers or 
access doors shall be clearly marked to indicate the 
voltage present. 

6.1.7 It is recommended to provide at least two 
lighting sub-circuits in each house. It is also 
recommended that a separate lighting circuit be 
utilized for all external lighting of steps, walkways, 
driveways, porch, car park, terrace, etc., with a master 
double-pole switch for the sub-circuit in addition to 
the individual switches. 

6.1.8 Wherever the load to be fed is more than 1 kW, it 
shall be controlled by an isolator switch or miniature 
circuit-breaker. 

6.2 Selection of Wiring 

Any one of the following types of wiring may be used 
in a residential building (see Part 1/Section 9 of this 
Code). 

a) Tough rubber sheathed or PVC insulated PVC 
sheathed wiring on wood batten, 

b) PVC insulated wiring in steel/non-metallic 
surface conduits, and 

c) PVC insulated wiring in steel7non -metallic 
recessed conduits. 

However, if aesthetics is the main consideration, 
recessed conduit wiring system may be adopted. 

The wiring for 16 A plug outlets (power circuits) shall 
invariably be carried out either in surface/recessed conduit 
wiring system where general wiring is on wood batten. 



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Wiring for staircase lights and garage lights may be 
done in recessed conduit wiring systems. 

7 SWITCHGEAR FOR CONTROL AND 

PROTECTION 

7.1 Location 

7.1.1 All main switches or miniature circuit-breakers 
shall be either of metal-clad enclosed pattern or of any 
insulated enclosed pattern which shall be fixed at close 
proximity to the point of entry of supply. 

7.1.2 Open type switch boards shall be placed only in 
dry situation and in well ventilated rooms. They shall 
not be placed in the vicinity of storage batteries and 
exposed to chemical fumes. 

7.1.3 Main switch boards shall be installed in rooms 
or cupboards having provision for locking so as to 
safeguard against operation by unauthorized persons. 

7.1.4 In a damp situation or where inflammable or 
explosive dust, vapour or gas is likely to be present, 
the switch boards shall be totally enclosed or made 
flame-proof as may be necessitated by the particular 
circumstances. 

7.1.5 Switch boards shall not be erected above gas 
stoves or sinks or within 2.5 m of any washing unit in 
the washing room. 

7.1.6 Switch boards, if unavoidably fixed in places 
likely to be exposed to weather, to drip, or to abnormal 
moist atmosphere, their outer casing shall be 
weatherproof and shall be provided with glands or 
bushings or adopted to receive screwed conduit 
according to the manner in which cables are run. PVC 
and double flanged bushes shall be fitted in the holes 
of the switches for entry and exit of wires. 

7.1.7 A switch board shall not be installed so that its 
bottom is within 1.25 m above the floor, unless the 
front of the switch board is completely enclosed by a 
door, or the switch board is located in a position to 
which only authorized persons have access. 

7.1.8 Where so required, the switch boards shall be 
recessed in the wall. The depth of recess provided at 
the back for connection and the space at the front 
between the switchgear mountings shall be adequate. 

7.1.9 Equipment's which are on the front of a 
switchboard shall be so arranged that inadvertent 
personal contact with live parts is unlikely during the 
manipulation of switchgears, changing of fuses or 
similar operations. 

7.1.10 No mounting shall be mounted within 2.5 cm 
of any edge of the panel and no hole other than the 
holes by means of which the panel is fixed shall be 
drilled closer than 1.3 cm from any edge of the panel. 



7.2 General Requirements of Switchboards 

7.2.1 The various live parts, unless they are effectively 
screened by insulating material shall be so spaced that 
an arc cannot be maintained between such parts and 
earth. 

The arrangement of the gear shall be such that they 
shall he readily accessible and their connections to all 
instruments and apparatus shall also be traceable. 

7.2.2 In every case in which switches and fuses are 
fitted on the same pole, these fuses shall be so arranged 
that the fuses are not alive when their respective 
switches are in the 'off position. 

7.2.3 No fuse other than fuses in instrument circuit 
shall be fixed on the back of or behind a switchboard 
panel or frame. 

7.2.4 All metal switchgears and switchboards shall be 
painted and maintained during service. 

7.2.5 All switchboards connected to medium voltage 
and above shall be installed in accordance with 
Part 1/Section 9 of this Code. 

7.2.6 The wiring throughout the installation shall be 
such that there is no break in the neutral wire in the 
form of a switch or fuse unit. 

7.2.7 The neutral shall also be distinctly marked. 

7.2.8 The main switch shall be easily accessible. 

7.3 Types of Switchboards 

7.3.1 In dwelling units, the metal clad switchgears shall 
preferably be mounted on any of the following types 
of boards: 

a) Hinged type metal boards — Such boards 
shall be suitable for mounting of metal clad 
switchgear consisting of not more than one 
switchgear and ICDB 4 way or 6 way, 15 A 
per way. 

b) Fixed type metal boards — Such boards shall 
be suitable for large switchboards for 
mounting large number of switchgears and 
or higher capacity switchgear. 

c) Wooden hoards — For small installations 
connected to a single phase 240 V supply, 
these boards may be used as main board or 
sub-boards. These shall be of seasoned and 
durable wood with solid back impregnated 
with varnish with joints dove-tailed. 

NOTE — See also Part 1/Section 9 of this Code. 

Where a board has more than one switchgear, each 
such switchgear shall be marked to indicate the section 
of the installation it controls. The main switchgear shall 
be marked as such. Where there is more than one main 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



207 



SP 30 : 2011 



switchboard in the building, each switchboard shall 
be marked to indicate the section of the installation 
and building it controls. 

7.4 Distribution Boards 

7.4.1 Distribution boards shall preferably be of metal 
clad type. 

7.4.2 Main distribution boards shall be controlled by a 
linked switchfuse or circuit-breaker. Each outgoing 
circuit shall be provided with a fuse on the phase or 
live conductor. 

7.4.3 Branch distribution boards shall be controlled 
by a switchfuse or circuit-breaker. Each outgoing 
circuit shall be provided with a fuse MCB on the phase 
or live conductor. The earthed neutral conductor shall 
be connected to a common link and be capable of being 
disconnected individually for testing purposes. At least 
one spare circuit of the same capacity shall be provided 
on each branch distribution board. 

7.4.4 Triple pole distribution boards shall not 
generally be used for final circuit distribution. Where 
use of triple pole distribution boards is inevitable, 
individual single phase circuit shall be controlled by 
double pole isolator. 

7.4.5 All distribution boards shall be marked 'Lighting' 
or Tower' as the case may be and also with the voltage 
and number of phases of the supply. 

7.4.6 The distribution boards for light and power 
circuits shall be different. 

8 SERVICE LINES 

The relevant provisions of IS 8061 shall apply. 

9 METERING 

9.1 It is recommended to have two distinct circuits, 
one for lights and fans and the other for high wattage 
(power) appliances particularly when the tariff is 
different for light and power. 

9.2 Energymeters shall be installed at such a place 
which is readily accessible to both the owner of the 
building and the authorized representatives of the 
supply authority. These should be installed at a height 
where it is convenient to note the meter reading, it 
should preferably not be installed at a height less than 
1 m from the ground. The energymeters should either 
be provided with a protective covering, enclosing it 
completely, except the glass window through which 
the readings are noted or should be mounted inside a 
completely enclosed panel provided with a hinged or 
sliding doors with arrangement for locking it. The 
room/space where energy meters are installed shall be 
kept clear from any obstruction {see also IS 15707). 



9.3 Means for isolating the supply to the building shall 
be provided immediately after the energymeter. 

10 EARTHING IN DOMESTIC INSTALLATIONS 

10.0 Means shall be provided for proper earthing of 
all apparatus and appliances in accordance with 
Part 1/Section 14 of this Code. 

10.1 Plugs and Sockets 

All plugs and sockets shall be of three-pin type, one of 
the pins being connected to earth. 

10.2 Lighting Fittings 

If the bracket type lamp holders are of metallic 
construction, it is recommended that they should be 
earthed. All pedestal lamp fittings of metallic 
construction shall be earthed. 

10.3 Fans and Regulators 

Bodies of all table fans, pedestal fans, exhaust fans, 
etc., shall be earthed by the use of three-pin plugs. The 
covers of the regulators, if of metallic construction shall 
be earthed by means of a separate earth wire. 

10.4 Domestic Electric Appliances 

Bodies of hot-plates, kettles, toasters, heaters, ovens 
and water boilers shall all be earthed by the use of 
three-pin plugs. However, if fixed wiring has been used, 
then a separate earth wire shall be used for earthing 
these appliances. 

10.5 Bath Room 

The body of automatic electric water heaters shall be 
earthed by the use of a three-pin plug or by a separate 
earth wire, if fixed wiring has been done. All non- 
electrical metal work including the bath tub, metal 
pipes, sinks and tanks shall be bonded together and 
earthed. 

10.6 Radio Sets 

From the point of view of good reception it is 
recommended that radio sets should be earthed through 
an electrode different from that of the main earth 
system for other electrical appliances. However, if it is 
not possible to have separate earth electrode, radio sets 
may be earthed through the main earth system. 

10.7 Miscellaneous Apparatus 

Where appliances utilizing gas and electricity are in 
use, for example, gas-heated electricity-driven washing 
machines, the inlet end of the gas supply shall be either 
fitted with a strong insulating bush, substantial enough 
to stand a flash test of 3 500 V and so designed as to 
be difficult to detach, or, where it is desirable or 
necessary that metal work in proximity to electrical 



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apparatus be bonded to the earthed metal work of the 
latter, as for example, in kitchens, the gas supply shall 
be introduced through a non-conducting plastic pipe 
from a point not in proximity to earthed metal work. 
Where separation is not easily achieved, for example, 
as in cases of direct-coupled motor-driven gas boosters 
and motorized gas valves, the metal work of the 
electrical equipment, shall be bonded to the metal or 
pipework of gas equipment. In such cases the addition 
to the motor control gear of a differential or current- 
balance type of circuit-breaker, designed to operate at 
low values of fault current, would afford a desirable 
safeguard against fault current transfer specially where 
the rating of the plant is of a size and capacity which 
entails correspondingly high ratings for the normal 
overload protective devices. 

The refrigerators, air-conditioners and coolers, electric 
radiators, electric irons, etc, shall all be earthed by the 
use of three-pin plugs. 

11 BUILDING SERVICES 

11.1 Lighting 

The general rules laid down in Part 1/Section 1 1 of 
this Code shall apply. The choice of lamps, lighting 
fittings shall be based on the recommended values of 
illumination given in Table 3. See SP 72 for detailed 
guidance. 

Tabfie 3 Recommended Levels of Illumination for 

Different Parts of Domestic Dwellings 
(Clauses 11.1 and 14.3) 



SI No. 


Location 


Illumination Level 

lux 


(1) 


(2) 


(3) 


i) 


Entrances, hallways 


100 


ii) 


Living room 


300 


iii) 


Dining room 


150 


iv) 


Bedroom: 






a) General 


300 




b) Dressing tables, bed heads 


200 


v) 


Games or recreation room 


100 


vi) 


Table games 


300 


vii) 


Kitchen 


200 


viii) 


Kitchen sink 


300 


ix) 


Laundry 


200 


x) 


Bathroom 


100 


xi) 


Bathroom mirror 


300 


xii) 


Sewing 


700 


xiii) 


Workshop 


200 


xiv) 


Stairs 


100 


xv) 


Garage 


70 


xvi) 


Study 


300 



11.2 Air-conditioning 

11,2.1 The general rules laid down in Part 1/Section 1 1 
of this Code shall apply. For domestic dwellings, by 



and large, the following types of air-cooling equipment 
are used: 

a) Evaporative coolers, 

b) Packaged air-conditioners, and 

c) Room air-conditioners. 

11.2.2 The power requirements, layout and design of 
electrical installation shall take into account the number 
and type of such equipment. 

11.3 Lifts 

11.3.1 Whenever lifts are required to be installed in 
residential buildings, the general rules laid down in 
Part 1/Section 11 of this Code shall apply. However, 
the design of lifts shall take into account the following 
recommendations. 

11.3.1.1 Occupant load 

For residential (domestic) dwellings, the occupant load 
(the number of persons within any floor area) expressed 
in gross area in mVperson shall not be less than 12.5. 

11.3.1.2 Passenger handling capacity (H) 

Expressed as the estimated population that has to be 
handled in the buildings in the 5-minute peak period, 
the passenger handling capacity for residential 
buildings shall be 5 percent. 

11.3.1.3 Car speed 

Car speed for passenger lifts shall be as follows: 

a) In low and medium class flats 0.5 m/s, and 

b) Large flats (No. of floors served 6-12) 
0.754.5 m/s. 

11.3.2 Where a lift is arranged to serve two, three or 
four flats per floor, the lift may be placed adjoining 
the staircase, with the lift entrances serving direct on 
to the landings. Where the lift is to serve a considerable 
number of flats having access to balconies or corridors, 
it may be conveniently placed in a well ventilated tower 
adjoining the building. 

12 FIRE PROTECTION 

The following protection systems are recommended: 

a) One or two family private dwellings — Fire 
detection/extinguishing systems not required. 

b) Apartment houses/flats 

1) Up to 2 storey — Not required. 

2) 3 storey and above 

i) Floor area less than 300 m 2 — Not 

required, 
ii) Floor area more than 300 m 2 — 

Manually operated electric fire alarm. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



209 



SP 30: 2011 



SP 7 may be referred for detailed guidance. 

13 TESTING OF THE INSTALLATION 

The provisions of Part 1/Section 13 of this Code shall 
apply. 

14 MISCELLANEOUS PROVISIONS 

14.1 Telephone Wiring 

Facilities for telephone wiring shall be provided in all 
residential buildings where telephones are likely to be 
installed. In high rise residential buildings, a riser of 
adequate size shall be provided for telephone wiring 
cables. 

14.2 Safety Requirements 

Some of the important safety requirements in electrical 
installations in domestic dwellings are summarized 
below: 

a) All outlets for domestic electrical appliances 
shall be of three-pin socket type, third socket 
being connected to the earth. 

b) All the single pole switches shall be on phase 
or live conductor only. 



c) The electrical outlets for appliances in the 
bathrooms shall be away from the shower or 
sink (see Annex A). 

d) Wiring for power outlets in the kitchen shall 
be preferably done in metallic conduit wiring. 

e) The electrical outlets shall not be located 
above the gas stove. 

f) The clearance between the bottom most point 
of the ceiling fan and the floor shall be not 
less than 2.4 m. 

g) The metallic body of the fan regulator if any, 
shall be earthed effectively. 

h) Earth leakage circuit-breaker at the intake of 
power supply at the consumer's premises (see 
Part 1/Section 14 of this Code) shall be 
provided. 

14.3 Guidelines on Power Factor Improvement in 
Domestic Dwellings 

General guidelines on principal causes of low power 
factor and methods of compensation are given in 
Part 1/Section 17 of this Code. For guidance on natural 
power factor available for single phase appliances and 
equipment in domestic use, see Table 3. 



ANNEX A 

[Clause 14.2 (c)] 

PARTICULAR REQUIREMENTS FOR LOCATIONS CONTAINING A BATH TUB OR 

SHOWER BASIN 



A-l SCOPE 

The particular requirements of this Annex apply to bath 
tubs, shower basins and the surrounding zones where 
susceptibility of persons to electric shock is likely to 
be increased by a reduction in body resistance and 
contact with earth potential. 

A-2 CLASSIFICATION OF ZONES 

A-2.1 The requirements given in this Annex are based 
on the dimensions of four zones as described in Fig. 1 

and Fig. 2. 

a) Zone — is the interior of the bath tub or 
shower basin. 

b) Zone 1 — is limited: 



1) by the vertical plane circumscribing the 
bath tub or shower basin, or for a shower 
without basin, by the vertical plane 0.6 m 
from the shower head; and 

2) by the floor and the horizontal plane 
2,25 m above the floor. 

c) Zone 2 — is limited: 

1) by Zone 1 and the vertical parallel plane 
0.60 m external to Zone 1, and 

2) by the floor and horizontal plane 2.25 m 
above the floor. 

d) Zone 3 — is limited: 

1) by Zone 2 and the parallel vertical plane 
2.40 m external to Zone 2, and 



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NATIONAL ELECTRICAL CODE 



SP 30: 2011 



2) by the floor and the horizontal plane 

2.25 m above the floor. 

NOTE — The dimensions are measured taking account 
of walls and fixed partition. 

A-3 PROTECTION FOR SAFETY 

A-3.1 Where safety extra low voltage is used, whatever 
the nominal voltage, protection against direct contact 
shall be provided by: 

a) barriers or enclosures affording at least the 
degree of protection IP2X, or 

b) insulation capable of withstanding a test 
voltage of 500 V for 1 min. 

A-3.2 A local supplementary equipotential bounding 
shall connect all extraneous conductive parts in Zones 
1, 2 and 3 with protective conductors of all exposed 
conductive parts situated in these zones. 

A-4 SELECTION OF EQUIPMENT 

A-4.1 Electrical equipment shall have at least the 
following degrees of protection: 

a) Zone : IP X 7 

b) Zone 1: IPX 5 



c) Zone 2 : IP X 4 

d) Zone 3 : IP X 1 



IP X 5 in public baths 



A-4.2 In Zones 0, 1 and 2, wiring systems shall be limited 
to those necessary to the supply of appliances situated 
in those zones. Junction boxes are not permitted in Zones 
0, 1 and 2. In Zone 3, they are permitted if the necessary 
degree of protection is available. 

A-4.3 In Zones 0, 1 and 2 no switchgear and accessories 
shall be installed. 

A-4.4 In Zone 3, socket-outlets are permitted, only if 
they are either: 

a) supplied individually by an isolating 
transformer, or 

b) supplied by safety extra-low voltage, or 

c) protected by a residual current protective device. 

A-4.S Any switches and socket outlets shall be at a 
distance of at least 0.60 m from door of the shower 
cabinet. 

A-4.6 In Zone 0, only electrical appliances specially 
intended for use in the bath tub are permitted. In Zone 1 
only water heaters may be installed. In Zone 2 only 
water heaters and Class II luminaries may be installed. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



211 



SP 30 : 2011 



Bath Tub 




ZONE 2 * ZONE 3 

I 



e 

cm 



:^nix 



0.8 m 



ZONE 1 

Shower Basin 

.ZONE 1 ] ZONE 2 

o »- | 

M z z I 
M o o 



Y, Y ,1 Y ,Y V V \ V \ \*m\,} 



TTT 



2.40 m 



' ZONE 3 






Shower without Basin but with fixed partition 



1 



ZONE 1 



0.6 m 



\ \ \ \ \ \ 




ZONE 3 



£ 
to 

& 

CM 



^S^^^CE^TE^^C^ 



TT 



FIXED PARTITION WALL 



Fig. 1 Zone Dimensions (Elevation) 



212 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



£2, 



roi 



UJ 

z: 

o 

M 



UJ 

M 



a) Bath Tub 



b) Bath Tub with flxea Partition 



I 

ZONEI ZONE 3 
2 i 
i 



JLfir?^ 2.40m 



_^-" 



-#J 




c> Shower Basin 



ZONE 



f 

ZONEizone 3 



4- •*.-* 



i 
i 
i 



d) Shower Basin with Fixed Partition 



^^^^2 



ZONE 

'o 



zaszx szzzza 



V 0.6m ,' 



Z ° NE JZ0NE 3 ( 
1 ! 2.40m 

♦*• : 



e) Shower without Basin 



SHOWER \ \ [ 



f) Shower without Basin but with Fixed Partition 

-SHOWER HEAD 





Fig. 2 Zone Dimensions (Plan) 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



213 



SP 30: 2011 

SECTION 2 OFFICE BUILDINGS, SHOPPING AND COMMERCIAL CENTRES 

AND INSTITUTIONS 



FOREWORD 

Office buildings, shopping and commercial centres can 
be of various types depending on the size of the civil 
structure or the extent of activity involved in the 
building. High-rise buildings housing office complexes 
are common, calling for a coordinated planning while 
designing the electrical services therein. 

In small buildings with comparatively moderate loads, 
supply is normally at medium voltage and the 
distribution of power is less complex. However, in the 
case of multi- storied office-cwm-commercial complex, 
where the large number of amenities is to be provided 
calls for a more complex distribution system. Some of 
such buildings has to incorporate a standby/emergency 
power plant for essential service needs. 

For editorial convenience, and keeping in view the 
similarly with the type of buildings covered in this 
section, educational and other institutional buildings 
are also covered here. Should any special provisions 
apply to them, they are identified at the relevant clauses. 

It is not possible to define strictly the type of buildings 
covered in this Section except in broad terms, an 
attempt has been made to identify the nature of the 
occupancy. Reference may, however, be made to 3 
wherein a description is provided for the various types 
of installations covered in this Section. 

1 SCOPE 

This Part 3/Section 2 of this Code covers requirements 
for electrical installations in office buildings, shopping 
and commercial centres and educational and similar 
institutional buildings. 

2 REFERENCES 

This Part 3/Section 2 of the Code should be read in 
conjunction with the following Indian Standards: 



IS No. 
3646 (Part 2) : 1966 



8061 : 1976 



15707 : 2006 



Title 
Code of practice for interior 
illumination: Part 2 Schedule for 
values of illumination and glare 
index 

Code of practice for design, 
installation and maintenance of 
service lines upto and including 
650 V 

Testing, evaluation, installation 
and maintenance of ac electricity 
meters — Code of practice 



3 TERMINOLOGY 

For the purpose of this Section, the definitions given 
in Part 1/Section 2 of this Code shall apply. 

4 CLASSIFICATION 

The electrical installations covered in this Section, are 
those in buildings intended for the following purposes: 

a) Office Buildings/Business Buildings — These 
include buildings for the transaction of business, 
for the keeping of accounts and records and 
similar purposes, professional establishments, 
offices, banks, research establishments, data 
processing installations, etc. 

b) Shopping/Commercial Centres/Mercantile 
Buildings — These include buildings used as 
shops, stores, market, for display and sale of 
merchandise, wholesale or retail, 
departmental stores, etc. 

c) Educational Buildings — These include 
buildings used for schools, colleges and 
daycare purposes for more than 8 hours per 
week involving assembly of people for 
instruction and education (including 
incidental recreation), etc. 

NOTE — Larger assembly buildings recreational 
occupancies are covered in Part 3/Section 3 of this Code. 

5 GENERAL CHARACTERISTICS OF 
INSTALLATIONS 

5.0 General guidelines on the assessment of 
characteristics of installations in buildings are given 
in Part 1 /Section 8 of this Code. For the purpose of 
installations falling under the scope of this Section the 
characteristics defined below generally apply. 

5.1 Environment 

The following environmental factors shall apply to 
office buildings, shopping and commercial centres and 
educational/institutional buildings. 



Environment 


Characteristics 


Remarks 


(i) 


(2) 


(3) 


Presence of 


Probability of 




water 


presence of water 
is negligible 




Presence of 


The quantity or 




foreign solid 


nature of dust or 




bodies 


foreign solid 
bodies is not 
significant 





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Environment 
(1) 



Characteristics 
(2) 



Remarks 

(3) 



Utilization 

(i) 



Characteristics 
(2) 



Remarks 
(3) 



Presence of 
corrosive or 
polluting 
substances 



The quantity and 
nature of 
corrosive or 
polluting 
substances is not 
significant 



Mechanical 
stresses 

Seismic effect 
and lighting 



Impact and 
vibration of low 
severity 



Locations where 
some chemical 
products are 
handled in small 
quantities, (for 
example, labora- 
tories in schools 
and colleges) will 
be categorized as 
AF3. For office 
and other build- 
ings covered by 
this Section 
situated by the sea 
or in industrial 
zones, producing 
serious pollution, 
the categorization 
AF2 applies (see 
Part 3/Section 8) 



Depends on the 
location of the 
building 



5.2 Utilization 

The following aspects of utilization shall apply: 



Utilization 


Cha racteristics 


Remarks 


(1) 


(2) 


(3) 


Capability of 


Uninstructed 


A major percentage 


persons 


persons 


of occupants 




Children 


Applies to schools 




Persons 


Applies to areas 




adequately 


such as building 




advised or 


substations and for 




supervised by 


operating and 




skilled persons 


maintenance staff 


Contact of 


Persons in non- 




persons 


conducting 
situations 




Conditions of 


Low density 


Small offices and 


evacuation 


occupation, easy 


shops 


during 


conditions of 




emergency 


evacuation. 






High density 


Departmental stores 




occupation, 






difficult 






conditions of 






evacuation 






High density 


High rise office 




occupation, 


commercial centres, 




difficult 


underground 



Nature of 
processed of 
stored material 



conditions of 
evacuation 
No significant 
risks 

Existence of 
fire risk 



shopping arcades, 

etc 

Small shops 



In view of large 
volume of paper 
and furniture, for 
example, office 
buildings, furni- 
ture shops, etc. 



6 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

6.0 Exchange of Information 

6,0.1 Proper coordination shall be ensured between the 
architect, building contractor and the electrical engineer 
on the various aspects of installations design. From 
the point of view of the design of the various 
installations, the following shall be considered. 

a) Maximum demand and diversity; 

b) Type of distribution system, mains and sub- 
mains; 

c) Nature of supply (current, frequency, nominal 
voltages); 

d) Prospective short-circuit current at the supply 
intake point; 

e) Division of the installation; 

f) Nature of the external influences (see 4); 

g) Maintainability of the installations; 

h) Nature and details of building services; 

1) Lighting, 

2) Air-conditioning, and 

3) Lifts. 

j) Other details as relevant such as, pumps for 
fire fighting, lighting, fire-alarm systems, 
telephones, call-bells, clock systems, etc; 

k) Telephone circuits including extensions and 
intercom facilities; 

m) CCTV for information display and security; 

n) Computer installation facility where 
applicable; and 

p) Metering system for different loads. 

NOTE — Fire protection system shall include such 
details such as locations of detectors, zonal indicators, 
central control console, public address system for fire 
fighting, cable runs and their segregation from the other 
cable system. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



215 



SP 30: -2011 



A complete drawing of layout of the electrical 
installation shall be prepared together with associated 
floor plans indicating the details mentioned in (a) to 
(p). This wiring diagram shall include outlets for lights, 
sockets, bells, ceiling fans, exhaust fans, location of 
sectionalized control switches, distribution boards, etc. 
In special occupancies such as school or college 
laboratories, the dc circuits be identifiable in the layout 
diagram. 

6.1 Branch Circuits 

6.1.1 The general design of wiring of branch circuits 
shall conform to those laid down in Part 1 /Section 1 1 
of this Code. However, for special cases such as for 
communication networks, fire-alarm system and wiring 
for data-processing equipment, the recommendations 
of the manufacturer shall apply. 

6.1.2 The branch circuit calculations shall be done 
according to the general provisions laid down in Part 3/ 
Section 1 of this Code. However, the specific demands 
of the lighting, appliance and motor loads as well as 
special loads encountered in the types of buildings 
covered in this Section shall be taken into account. 

6.1.3 In offices and showrooms, the interior decoration 
normally include false ceiling, carpets and curtails. Any 
wiring laid above the false ceiling should be adequately 
protected such as by drawing the wires in metallic 
conduits and nor run in open. Wires shall not be covered 
by carpets. They shall be run at skirting level and 
encased for mechanical protection. 

6.1.4 Adequate number of socket-outlets shall be 
provided for electrically operated office machines such 
as electrical typewriter, calculators, etc, to avoid 
training of wires and use of multiple outlets from one 
socket. 

6.1.5 Areas where corrosive or polluting substance are 
present intermittently or continuously, such as school 
laboratories and other buildings located in high 
industrial pollution zones, socket-outlets shall 
preferably be of metal clad weatherproof type with 
covers. 

6.1.6 Lighting circuits shall preferably be combined 
in switched groups so that lighting can be limited to 
desks which are occupied. 

6.2 Service Lines 

The general provisions laid down in IS 8061 shall 
apply. 

6.3 Building Substations 

6.3.0 General 

The designer of power supply for office buildings and 
commercial centres shall take into account the great 



concentration of power demand of the electrical loads. 
Air-conditioning in office buildings absorbs an 
especially high proportion of the total power used. 
Consequently, such occupancies have to be provided 
with their own substation with vertical and horizontal 
forms of power distribution. 

6.3.1 If the load demand is high, requiring supply at 
high voltage, accommodation for substation equipment 
will be required. Main switch room will serve feeders 
to various load centres such as air-conditioning plant, 
elevators, water pumps, etc. Other loads are taken to 
local distribution boards. 

6.3.2 The transformer power rating for the supply of 
the building shall be sufficient to cater to the highest 
simultaneous power requirements of the building. 
Typical proportions of power usage are given as 
follows: 



Part of Electrical 


Part of the Total 


Diversity 


Installation 


Power Requirement 
Percent 


Factor 


(1) 


(2) 


(3) 


Ventilation, heating 


45 


1.0 


(air-conditioning) 






Power plant (drives) 


5 


0.65 


Lighting 


30 


0.95 


Lifts 


20 


1.0 



63.3 The location and layout of building substation 
shall conform to the general rules laid down in Part 2 
of this Code. The substation room shall be well 
ventilated and inaccessible to birds and reasonably 
reptile-, rodent- and insect-proof. Only authorized 
persons be allowed to enter the substation for 
operations/maintenance of any kind. Cables leading 
from the substation to the main building shall 
preferably be carried underground through ducts or 
pipes of adequate dimensions. Such pipes shall be 
properly sealed at both ends to reduce the possibility 
of rain water flowing through the pipes and flooding 
the trenches. 

6.3.4 Emergency Supply 

Wherever emergency supply is considered necessary, 
it can be in the form of separate and independent feeder 
from the undertaking terminated in equipment isolated 
from the regular supply line. In case of standby supply 
from diesel generator set, it will be installed as per the 
general rules laid down in Part 2 of this Code. 

6.3.4.1 In office buildings, certain safety and essential 
services shall be supplied even in the case of mains 
failure. These are governed by the rules and regulations 
of the respective authorities. Essential services include 
amongst others, water-pressure pumps, ventilation 



216 



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SP 30 : 2011 



installations, essential lighting and lifts. The power 
requirement of these essential loads is generally about 25 
percent of the total power requirement of the building. 

6.3.5 Switchboards and Panel Boards 

All current carrying equipment shall be totally 
enclosed, dust-and vermin-proof and if mounted 
outdoor, shall be of weatherproof construction or 
housed in weatherproof kiosk or cabin. Switchboards 
shall be of open type or cubicle type. Cubicle type 
boards shall be with hinged doors interlocked with 
switch-operating mechanisms. All switches shall bear 
labels indicating their functions. Switchboards shall 
be located away from areas likely to be crowded by 
the public. 

6.3.6 Selection of equipment shall be made according 
to the guidelines laid down in Part 1 /Section 9 of this 
Code. For the purposes of office buildings, shopping 
and commercial centres, miniature circuit-breakers of 
adequate capacity shall be preferred to switchfuse units. 
They can also be effectively used in place of fuses in a 
distribution board. 

6.4 Metering 

In multi-storied buildings, a number of offices, and 
commercial centres occupy various areas. Electrical 
load for each of them would have to be metered 
separately; the meter-room normally is situated in the 
ground floor (see IS 15707 for further guidance). 

6.5 System Protection 

6.5.0 General 

The general rules for protection for safety laid down 
in Part 1/Section 7 of this Code shall apply. Reference 
is also drawn to SP 7 on guidelines for fire protection 
of buildings. The general rules given below shall apply. 

6.5.1 The type of buildings covered in this Section fell 
under Group B (educational buildings). Group E 
(business buildings) and Group F (mercantile 
buildings) from the point of view of fire safety 
classification (see SP 7). Typical fire fighting 
installation requirements are also covered therein. The 
electrical needs for the appropriate type of installation 
shall, therefore, be decided accordingly. 

6.5.1.1 Educational buildings (Group B) 

Educational buildings above 2- storeys having an area 
of more than 500 m 2 per floor shall have besides fire- 
fighting equipment, manually operated electrical fire 
alarm and automatic fire alarm systems. 

6.5.1.2 Business buildings (Group E) 

Besides fire-fighting equipment, automatic fire alarm 
systems are recommended for offices, banks, 



professional establishments, etc, where the buildings 
are more than 2 storey with floor area above 500 m 2 
per floor, and for laboratories with delicate instruments 
as well as computer installations. 

6.5.1.3 Mercantile buildings (Group F) 

Besides fire-fighting equipment, automatic sprinkles 
and automatic fire alarm systems are recommended 
for wholesale establishments, warehouses, transport 
booking agencies, etc, as well as for shopping areas 
inside buildings with area more than 500 m 2 on each 
floor. For other premises and shopping lines with 
central corridors open to sky, automatic fire-alarm 
systems shall be installed. Underground shopping 
centres shall be provided with automatic sprinkles. 

6.6 Building Services 

6.6.1 Lighting 

6.6.1.1 The general rules laid down in Part 1/Section 1 1 
of this Code shall apply. The choice of lamps, lighting 
fittings and general lighting design together with power 
requirement shall be planned based on the 
recommended values of illumination and limiting 
values of glare index given in Table 1. 

6.6.1.2 In commercial premises, a fairly high level of 
glare free lighting on working planes and subdued 
lighting in circulation areas are necessary. Aesthetics 
and interior decoration also play a part. Lighting design 
in showrooms includes high level of lighting in the 
vertical and horizontal planes, depending on the 
merchandise exhibited and their layout. Colour 
temperature characteristics of the light source shall 
also be taken into account in the case of showroom 
lighting. 

6.6.2 Air-conditioning 

6.6.2.1 The general rules laid down in Part 1/Section 14 
of this Code shall apply. The design of the air- 
conditioning system, shall take into account the 
requirements stipulated in the following clauses. 

6.6.2.2 In case of large air-conditioning installations 
(500 tonne and above) it is advisable to have a separate 
isolated equipment room together with electrical 
controls. All equipment rooms shall have provision for 
mechanical ventilation. 

6.6.3 Lifts and Escalators 

6.6.3.1 The general rules laid down in Part 1/ 
Section 14, of this Code shall apply. However, the 
design of lifts shall take into account the following 
recommendations : 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



217 



SP 30: 2011 



Table 1 Recommended Values of Illumination and Glare Index 

{Clause 6.6.1) 



SSNo. 



(l) 



BuiBding 



(2) 



Illumination 


Limiting Glare Index 


lux 






(3) 




(4) 


300 ■ 




19 


150 




19 


70-150 






150-300 




19 


300-700 




22 


300-700 




22 


150-300 




19 


150 






300 




19 


300 




19 


450 




19 


450 




16 


70 




— 


100 




— 


100 




— 


200 




16 


150 




25 


150 




16 


300 




16 


300 




16 


300 




16 


200-300 




— 


700 




10 


450 




16 


{see SI No. ii above.) 




[see appropriate trades 


in IS 3646 (Part 2)] 


300 




19 


150 




19 


70 




— 


100 




— 


150-300 




22 


200 




25 



Banks: 

a) Counters, typing accounting book areas 

b) Public areas 



ii) Libraries; 


a) 


Shelves 


b) 


Reading rooms (newspaper, magazines) 


c) 


Reading tables 


d) 


Book repair and binding 


e) 


Cataloging, sorting, stock rooms 


iii) Off 


ices: 


a) 


Entrance halls and reception area 


b) 


Conference rooms, executive offices 


c) 


Genera] offices 


d) 


Business machine operation 


e) 


Drawing offices 





Corridors and lift cars 


g) 


Stairs 


h) 


Lift landings 


J) 


Telephone exchanges; 




1) Manual exchange rooms (on desk) 




2) Main distribution frame room 


iv) Schools and colleges: 


a) 


Assembly halls: 




1) General 




2) When used for exams 




3) Platforms 


b) 


Class and lecture rooms: 




1) Desks 




2) Black board 


c) 


Embroidery and sewing rooms 


d) 


Art rooms 


e) 


Libraries 


f) 


Manual training 


g) 


Offices 


h) 


Staff rooms, common rooms 


J) 


Corridors 


k) 


Stairs 


v) Shops and stores^: 


a) 


General areas 


b) 


Stock rooms 



Does not cover display (showroom lighting). 



6.6.3.2 Occupant load 
These shall be as follows: 



5/ 


Occupancy 


Occupation 


No. 




Load Gross Area 
in m 2 /Person 


(1) 


(2) 


(3) 


i) 


Educational 


4 


ii) 


Business 


10 


iii) 


Mercantile: 






1) Ground floor and sales 


3 




2) Upper sale floor 


6 



6.6.3.3 Passenger handling capacity (H) 

These are expressed in terms of percent of the estimated 
population that has to be handled in the building in the 
5 min peak period as follows: 



SI 
No. 
(1) 



Occupancy 

(2) 



H 

(Percent) 
(3) 



i) Diversified (mixed) office occupancy 10-15 
ii) Single purpose office occupancy 15-25 



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6.6.3.4 Car speed — These shall be as follows: 



SI 


Occupancy 


No. of 


Car 


No. 




Floors 


Speed 






Served 


20 m/s 


(1) 


(2) 


(3) 


(4) 


i) 


Office building 


4-5 


0.5-0.75 






6-12 


0.75-1.5 






13-20 


Above 1.5 


ii) 


Shops and departmental 

stores 




2-2.5 



6.6.3,5 For office buildings, it is desirable to have at 
least a battery of 2 lifts at two or more convenient 
points. If this is not possible, it is advisable to have at 
least two lifts side by side at the main entrance and 
one lift each at different sections of the building for 
inter-communication. When two lifts are installed side 
by side, the machine room shall be suitably planned. 
All machines and switchgear may be housed in one 
machine room. 

7 TESTING OF INSTALLATION 

The various tests on the installation shall be carried 
out as laid down in Part 1/Section 13 of this Code. 

8 MISCELLANEOUS PROVISIONS 

8.1 Group Control 

8.1.1 The lighting circuits shall preferably be combined 
in switched groups as well as coordinated to functional 
groups of desks in an open plan office. The switching 
points may be combined centrally at the entrance 
passageways. In order to ensure proper co-ordination 
with design of the building for daylight use of devices 
such as photoelectric switches shall be encouraged for 
controlling lighting groups near windows. 

8.2 Telephones/Intercoms 

8.2.1 Adequate coordination shall be ensured right from 
the planning stages with the telephone authorities to 
determine the needs for the telephone system catering 
to the various units in office buildings. For private 
intercom systems, entirely under the control of the user, 
it is necessary to pre-plan the coordination of external 
and intercom systems. 

8.3 Electric Call Bell System 

8.3.1 The general guidelines laid down in Part 1/ 
Section 11, regarding installation of electric bells and 
call system shall be referred to. Depending on the final 
requirements of the type of occupancy, the type of 
equipment to be used, wiring and other details shall be 
agreed to. 



8.3.2 A simple call bell system is suitable for small 
offices whereby service staff may be called to a 
particular position by the caller. A visible- cwm-audible 
indicator/bell panel shall be used. When call points are 
too numerous on a single indicator panel, such as in 
large offices, multiple call system shall be preferred. 
The layout in such a case would be determined by the 
size of building and staff. Time bell systems shall be 
installed in schools to give Start-work and Stop-work 
signals. 

8.4 Clock Systems 

8.4.1 The general guidelines contained in Part 1/ 
Section 14 shall apply regarding installation and 
maintenance of master and slave clock systems. 

8.4.2 In simple installations, impulse clocks designed 
to operate at the same current may be connected in 
one series circuit, with a battery having sufficient 
voltage to ensure satisfactory operation. In a more 
complex installation like multi-storeyed office 
buildings with large number of slave clocks, the 
impulse clocks may be arranged in number of series 
circuits. Each of which is connected to a pair of 
contact on a relay which is operated from the contacts 
of master clock. 

8.4.3 Master clock shall be placed in a dust free 
location, readily accessible for maintenance at all 
times. 

8.5 Closed Circuit TV 

8.5.1 Commercial buildings may require the 
installations of CCTVs for one of more of the following 
purposes: 

a) Security, and 

b) Information display. 

Educational/institutional buildings may use CCTV as 
a teaching aid for pre-recorded educational 
programmes. Reference shall be made to good practice 
for installations of such facilities. 

8.6 Emergency Lights for Critical Areas 

Battery powered (at least 2 h rating) emergency lights 
should be installed at critical and strategic locations 
including emergency exit points. These will provide 
illumination by self contained battery source even on 
failure of a.c. mains. On resumption of a.c. power supply, 
they will switch back to mains automatically and 
simultaneous recharge the battery to the required level. 

8.7 Emergency Exit Signage 

Photo luminescent safety signage should be provided 
at different strategic locations. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



219 



SP 30 : 2011 



SECTION 3 RECREATIONAL, ASSEMBLY BUILDING 



FOREWORD 

A variety of buildings are being used for public assembly 
for purposes that are recreational, amusement, social or 
religious. These include cinema halls, theatres, auditoria 
and the like, the primary feature being a congregation 
of people of all age groups for a short period of time 
during a day or a group of days. Buildings such as those 
catering to display of regular programmes demands a 
continuous power supply. In view of the nature of use 
of such occupancies, certain specific safety and 
reliability considerations become necessary for the 
electrical installations. 

The lighting design of such buildings are generally 
sophisticated, required to be properly coordinated with 
the electro-acoustic demands. On the physical aspects 
of lighting and sound systems in recreational buildings, 
it is recommended that assistance should be derived 
from specialists as such details are beyond the scope 
of this Code. 

Sports buildings, which are also basically assembly 
buildings, are covered separately under Part 3/Sec 6 
of this Code, in view of their unique nature. The type 
of buildings covered in this Section are enumerated 
in 4. It shall also be noted that assembly buildings 
forming part of other building complex, say, 
educational or office-commercial-cum-cinema 
complex shall also comply with this Section. 

1 SCOPE 

1.1 This Part 3/Section 3 of the Code covers 
requirements for electrical installation in buildings, 
such as those meant for recreational and assembly 
purposes, 

1.2 This Part 3/Section 3 does not cover sports 
buildings. 

2 REFERENCES 

This Part 3/Section 1 of the Code should be read in 
conjunction with the following Indian Standards: 

IS No. Title 

8061 : 1976 Code of practice for design, 

installation and maintenance of 
service lines upto and including 
650V 

SP 72 : 2010 National Lighting Code 

3 TERMINOLOGY 

For the purpose of this Section, the definitions given 
in Part 1 /Section 2 of this Code shall apply. 



4 CLASSIFICATION 

4,1 The electrical installations covered in this Section, 
are those in buildings intended for the following purposes: 

Assembly/Recreational Buildings — These shall 
include any building where groups of people 
congregate or gather for amusement, recreation, social, 
religious, patriotic, civil and similar purposes, for 
example, theatres, motion-picture (cinema) houses, 
assembly halls, auditoria, exhibition halls, museums, 
restaurants, places of worship, dance halls, clubs, etc. 

NOTE — Theatres are also classified further as permanent (air- 
conditioned and non-air-conditioned), temporary or traveling 
depending on the nature or construction of the premises. 
Temporary installations shall also conform to the additional 
provisions laid down in Part 5/Section 2 of this Code. 

5 GENERAL CHARACTERISTICS OF 
INSTALLATIONS 

5.0 General guidelines on the assessment of 
characteristics of installations in buildings are given 
in Part 1/ Section 8 of this Code. For the purpose of 
installations falling under the scope of this section, the 
characteristics defined below generally apply. 

5.1 Environment 

The following environmental factors shall apply to 
recreational and assembly buildings: 

Environment Characteristics Remarks 

(1) (2) (3) 



Presence of 


Probability of 


— 


water 


presence of 
water is 
negligible 




Presence of 


The quantity or 


— 


foreign solid 


nature of dust or 




bodies 


foreign solid 
bodies is not 
significant 




Presence of 


The quantity 


— 


corrosive or 


and nature of 




polluting 


corrosive or 




substances 


polluting 
substances is 
not significant 




Mechanical 


Impact and 


— 


stresses 


vibration of low 
severity 




Seismic effect 


— 


Depends on the 


and lighting 




location of the 
building 



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5.2 Utilization 

The following aspects of utilization shall apply: 



Utilization 


Characteristics 


Remarks 


(1) 


(2) 


(3) 


Capability of Uninstructed persons 


Majority of 


persons 




the occupants 




Persons adequately 


Electrical 




advised or supervised by 


operating 




skilled persons 


areas 


Conditions 


High density occupation, 


Small theatres 


of evacuation easy conditions of 


and cinemas 


during 


evacuation 




emergency 








High density occupation 


Multiple 




difficult conditions of 


cinema halls, 




evacuation 


cultural and 

theatrical 

buildings 


Nature of 


Existence of fire risk 


In view of 


processed of 




large quantum 


stored 




of furniture 


material 




and drapings 



6 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

6.0 Exchange of Information 

6.0.1 Proper coordination shall be ensured between the 
architect, building contractor and the electrical engineer 
on the various aspects of the installation design in a 
building intended for recreational or assembly 
purposes. For large projects, the advice of the 
appropriate specialists shall be obtained, in particular 
on the following aspects: 

a) Audio- visual systems, 

b) Stage lighting and control, and 

c) General auditorium lighting and other special 
service needs. 

6.0.2 The installation work shall conform to the 
provisions of Indian Electricity Rules as well as other 
Rules applicable for assembly buildings formulated by 
the State Authorities. 

6.1 Branch Circuits 

6,1.0 The branch circuits shall in general cater to the 
following individual load groups: 

a) Power installation: 



1) Stage machinery, 

2) Ventilation and 
installation, 



air-conditioning 



3) Lifts, and 

4) Additional power connections. 

b) Lighting: 

1) In front of the theatre, such as general 
lighting of outdoor, foyer, corridors and 
stairs, and auditorium; and 

2) In the rear of the theatre for stage, work 
place dressing rooms, workshops and 
storehouses. 

c) Emergency supply. 

6.1.1 The electrical lighting of the main building shall 
have at least three separate and distinct main circuits 
as follows: 

a) For the enclosures (cabin) and hence through 
a dimmer regulator to the central lighting of 
the auditorium; 

b) For one-half of the auditorium, passage ways, 
stairways, exit and parts of the building open 
to the public; and 

c) For the remaining half of the auditorium, 
passage ways, stairways, exit and parts of the 
building open to the public. 

6.1.2 The control of the circuits in respect of the two 
halves of the auditorium referred to in 6.1.1 shall be 
remote from each other. 

6.1.3 The cabin shall be provided with two separate 
circuits, one feeding the cabin equipments and the other 
lights and fans. 

6.1.4 Wiring shall be of the conduit type. Ends of 
conduits shall enter and be mechanically secured to the 
switch, control gears, equipment terminal boxes, etc. 
Ends of conduits shall be provided with screwed bushes. 
Within the enclosure, all cables shall be enclosed in 
screwed metal conduits adequately earthed. PVC 
conduits may be used in the auditorium and other places. 

6.1.5 Temporary wiring shall not be allowed in cabin, 
rewinding room, queue sheds and similar places. 

6.1.6 The cabin equipment shall be accessible at all 
times. Nothing shall impede access to any part of the 
equipment or its controls. 

6.1.7 Linked tumbler switches shall not be used for 
the control of circuits. 

6.1.8 Branch and main distribution boards shall be 
mounted at suitable height not higher than 2 m from 
the floor level. A front clearance of 1 m should also be 
provided. 

6.1.9 Wood work shall not be used for the mounting of 
or construction of the framework for iron-clad switch 
and distribution boards and controlgear. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



221 



SP 30 : 2011 



6.1.10 All the lighting fittings shall be at a height of 
not less than 2.25 m. 

6.1.11 The single pole switches for the individual lights 
and fans shall be mounted on sheet steel boards suitably 
earthed. 

6.1.12 Suitable socket outlets with controls shall be 
provided on the side walls near the stage for tapping 
supply to screen motor; stage focusing lights, audio 
systems and portable lights. 

6.1.13 In the queue sheds, bulk head fittings shall be used. 6 * 5 s y stem Protection 



a) As there will be concentration and movement 
of people, the substation should be located 
away from the area where people and vehicles 
move about, preferably at the rear of the 
building. 

b) The substation should not be in the way of 
people and fire-fighting vehicles and 
personnel where they are likely to attend to 
an emergency. 



6.1.14 For outdoor lighting, water-tight fittings shall 
be used and fittings may be so mounted without 
spoiling the aesthetic view of the recreation buildings. 

6.1.15 The installation in a traveling cinema should 
generally conform to the above requirements and the 
building should be sufficiently away from the nearest 
conductor of power lines {see 3.2 of Part 1 /Section 7 
of this Code). 

6.1.16 The plug points shall be provided at a height of 
about 1.5 m from the floor, in assembly buildings. 

6.1.17 In case of travelling cinemas, the wiring for the 
open yard lighting shall be done with weather-proof 
cables threaded through porcelain reel insulators 
suspended by earthed bearer wire at a height of not 
less than 5 m from ground level. The reel insulators 
shall be spaced 0.5 m from each other. 

6.1.18 When a tapping is taken from the open yard 
wiring, it should be taken only at a point of support 
through porcelain connectors housed in a junction box, 
fixed to the supporting pole. 

6.2 Feeders 

6.2.1 Feeder circuits shall generally conform to the 
requirements laid down in Part 1 /Section 1 1 of this 
Code. 

6.2.2 Separate feeders shall be taken to air-conditioning 
units, lifts and the lighting and fan circuits. 

6.3 Service Lines 

Service lines shall conform to IS 8061. 

6.4 Building Substation 

6.4.0 The electrical power demand of an assembly 
building can vary from 30 kVA to more than 1 000 kVA 
according to the size of the building. Usually, supply 
at voltages above 1 kV is given for large theatres and 
auditoria. Building substations shall conform to the 
general requirements specified in Part 2 of this Code. 

6.4.1 The following aspects shall be taken note of while 
deciding the location of substation: 



6.5.0 The rules for protection for safety laid down in 
Part 1 /Section 7 of this Code shall apply. Reference 
may also be made to SP 7 on guidelines for fire 
protection of buildings. The general rules given below 
shall apply. 

6.5.1 The type of occupancies covered in this Section 
fall under Group D (assembly buildings) from the point 
of view of fire safety classification. Such occupancies 
can be further classified into groups depending on the 
capacity of the theatre [auditorium to hold the 
congregation {see SP 7)]. Typical fire-fighting installation 
requirements are also covered therein. The following shall 
be provided besides fire-fighting equipment: 

a) Building having a theatrical stage and fixed 
seats: 

1) Stage — Automatic sprinkler; and 

2) Auditoria, corridor, green rooms, canteen 
and storage Automatic fire-alarm system. 

b) Buildings without a stage but no permanent 
seating arrangement — Automatic fire alarm 
system. 

c) All other structures designed for assembly — 
Manually operated electrical fire-alarm 
system. 

6.6 Building Services 

6.6.1 Lighting 

The general rules laid down in Part 1 /Section 1 1 of 
this Code shall apply. The choice of lamps, lighting 
fitting and general lighting design together with power 
requirement shall be planned based on the 
recommended values of illumination and glare index 
given in Table 1 {see SP 72). 

6.6.2 Air-conditioning 

6.6.2.1 The general rules laid down in Parti/Section 1 1 
of this Code shall apply. 

6.6.2.2 In air-conditioned assembly buildings, inside 
temperature shall be 22 ± 2°C. 

6.6.2.3 Provisions shall be made to record the 
temperature inside the auditorium. 



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Table 1 Recommended Values of Illumination 

and Glare Index 
(Clause 6.6.1) 



SI 


Part of Building 


Illumination 


Limiting Value of 


No. 




lux 


Glare Index 


(1) 


(2) 


(3) 


(4) 


1. 


Assembly and concert: 








a) Foyers, auditoria 


100450 


— 




b) Platforms 


450 


— 




c) Corridors 


70 


— 




d) Stairs 


100 


— 


2. 


Cinemas: 








a) Foyers 


150 


— 




b) Auditoria 


50 


— 




c) Corridors 


70 


— 




d) Stairs 


100 


— 


3. 


Museums: 








a) General 


150 


16 




b) Display 


Special lighting 


16 


4. 


Art Galleries: 








a) General 


100 


10 




b) Paintings 


200 


10 


5. 


Theatres: 








a) Foyers 


150 


— 




b) Auditoria 


70 


— 




c) Corridors 


70 


— 




d) Stairs 


100 


— 




NOTE — The above is 


meant for general 


guidelines and 




does not include special lighting effects. 





6.6.2.4 In the event of a breakdown of the air- 
conditioning plant, alternate arrangements should be 
available for ventilation and air circulation. 

6.6.3 Lifts and Escalators 

The general rules laid down in Part 1/Section 11 of 
this Code shall apply. However, the design of the lifts 
shall take into account the following recommendations: 



a) 



Occupant load 

This shall be as follows: 



Occupancy 



Occupant Load, Gross 
Area (m 2 /Person) 
0.6 



b) 



Assembly halls with 

fixed or loose seats 

and dance floors 

Without seating 1.5 

facilities including 

dining rooms 

Passenger handling capacity and car speed 
As given in Part 3/Section 2 of this Code. 



7 TESTING OF INSTALLATIONS 

The various tests on the installations shall be carried 
out as laid down in Part 1/Section 13 of this Code. 



8 MISCELLANEOUS PROVISIONS 

8.1 Emergency Supply 
See also Part 2 of this Code. 

8.1.1 In all recreational and assembly buildings, 
sufficient number of emergency lights in all the 
locations which includes all the emergency exit. 

8.1.2 Battery powered (at least 2 h rating) emergency 
lights should be installed at critical and strategic 
locations to avoid catastrophic in case of total power 
failure. These will provide illumination by self 
contained battery source even on failure of a.c. mains. 
On resumption of a.c. power supply, they will switch 
back to mains automatically and simultaneous recharge 
the battery to the required level. 

8.1.3 Depending on the total capacity required for 
standby supply for the occupancy, suitable standby 
generator set shall be installed. The location and 
installation of the standby DG set should be in 
accordance with the norms specified in Part 2 of this 
Code. 

8.2 Stage Lighting 

On the stage of a theatre, a great number of spotlights, 
border lights, projectors, etc, are required for 
illumination, including portable light sources. The 
various possibilities of switching each fittings shall be 
kept in view while designing the lighting circuits. For 
same lighting schemes, dimmer-control equipment 
may be required. 

8.3 Group Control 

The lighting in the auditorium shall be suitably 
combined into control groups to facilitate group 
switching. In the special case of stage lighting control, 
the lighting operator shall have a good view of the stage 
in order to be able to follow the performance. 
Therefore, the control-room shall be situated in a 
convenient position. 

8.4 Audio- Visual System 

Installation of amplifying and sound distribution 
systems shall conform to the guidelines contained in 
Part 1/Section 11 of this Code! 

8.5 Luminous Sign 

Photo luminescent safety signage should be provided 
at different strategic locations. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUS TRIAL BUILDINGS 



223 



SP 30: 2011 



SECTION 4 MEDICAL ESTABLISHMENTS 



FOREWORD 

Hospitals in the country vary in size from simple 
premises used for medical purposes in villages to a 
well-equipped, multidisciplinary hospital in big cities. 
The lattser type will have several units functioning 
simultaneously with a variety of support services to 
cater to the needs of doctors and patients. 

Safety requirements for electrical equipment used in 
medical practice are covered IS 13450 series. 
Additional safety provisions in the electrical 
installations of medically used rooms and medical 
establishments are covered in this Section of the Code. 
This Section 4 is based on the following 
considerations: 

a) The patient may not be in a condition to react 
normally to the effects of hazardous events; 

b) The electrical resistance of the skin, which is 
normally an important protection against 
harmful electric currents is bypassed in certain 
examinations or treatments; 

c) Medical electrical equipment may often be 
used to support or substitute vital body 
functions, the breakdown of which may cause 
a dangerous situation; 

d) Specific locations in medical establishments 
where flammable atmosphere exists, call for 
special treatment; and 

e) Electric and magnetic interference may 
disturb certain medical examinations or 
treatments. 

1 SCOPE 

This Part 3/Section 4 of this Code applies to the 
electrical installations in medical establishments. This 
Section is also applicable to rooms for veterinary 
medicine and dental practice. 

2 REFERENCES 

This Part 3/Section 4 of the code should be read in 
conjunction with the following Indian Standards: 

IS No. Title 

3646 (Part 2) : Code of practice for interior 

1966 illumination : Part 2 Schedule for 

values of illumination and glare 

index 
7689 : 1989 Guide for the control of 

undesirable static electricity 
8061 : 1976 Code of practice for design, 

installation and maintenance of 



IS No. 



13450 (Parti): 

1994 /IEC 

60601-1 : 1988 
14665 (Part 1) : 

2000 



SP 7 : 2005 
SP 72 : 2010 



Title 

service lines upto and including 

650 V 

Medical electrical equipment : 

Part 1 General requirements for 

safety 

Electric traction lifts : Part 1 
Guidelines for outline dimensions 
of passenger, goods, service and 
hospital lifts 

National Building Code of India 
National Lighting Code 



3 TERMINOLOGY 

In addition to the definitions contained in Part 1/ 
Section 2 of this Code the following shall apply. 

3,1 Rooms 

3.1.1 Anaesthetic Room — Medically used room in 
which general inhalation anesthetics are intended to 
be administered. 

NOTE — Anaesthetic room comprises for instance the actual 
operating theatre, operating preparation room, operating plaster 
room and surgeries. 

3.1.2 Angiographic Examination Room — Room 
intended for displaying arteries or veins, etc, with 
contrast media. 

3 A3. Central Monitoring Room — Room in which the 
output signals of several patient monitors are displayed, 
stored or computed. 

NOTE — A centra] monitoring room is considered to be part 
of a Room Group, if a conductive connection (for example, by 
signal transmission lines) between the rooms of such a group 
exists. 

3.1,4 Central Sterilization Room — Room, not spatially 
connected to a medically used room, in which medical 
equipment and utensils are sterilized. 



3.1.5 Delivery Room - 
takes place. 



- Room in which the actual birth 



3.1.6 Endoscopic Room — Room intended for 
application of endoscopic methods for the examination 
of organs through natural or artificial orifices. 

Examples of endoscopic methods are bronchoscopic, 
laryngoscopy, cystoscopic, gastroscopic and similar 
methods, if necessary, performed under anaesthesia. 

3.1.7 Heart Catheterization Room — Room intended 
for the examination or treatment of the heart using 
catheters. 



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Examples of applied procedures are measurement of 
action potentials of the haemodynamics of the heart, 
drawing of blood samples, injection of contrast agents 
or application of pacemakers. 

3.1.8 Hemodialysis Room — Room in a medical 
establishment intended to connect patients to medical 
electrical equipment in order to detoxicate their blood. 

3.1.9 Hydrotherapy Room — Room in which patients 
are treated by hydrotherapeutic methods. 

Examples of such methods are therapeutic treatments 
with water, brine, mud, slime, clay, steam, sand, water 
with gases, brine with gases, inhalation therapy, 
electrotherapy in water 1 } , massage thermotherapy and 
thermotherapy in water 1} . 

Swimming pools for general use and normal bath- 
rooms are not considered as hydrotherapy rooms. 

3.1.10 Intensive Care Room — Room in which bed 
patients are monitored independently of an operation 
by means of electromedical equipment Body actions 
may be stimulated, if required. 

3.1.11 Intensive Examination Room — Room in which 
patients are connected for the purpose of intensive 
examination, but not for the purpose of treatment, 
simultaneously to several electromedical measuring or 
monitoring devices. 

3.1.12 Intensive Monitoring Room — Room in which 
operated patients are monitored, using electromedical 
equipment. Body actions (for example, heart 
circulation, respiration) may be stimulated, if required. 

3.1.13 Labour Room — Room in which patients are 
prepared (waiting) for delivery. 

3.1.14 Medical Establishment — Establishment for 
medical care (examination, treatment, monitoring, 
transport, nursing, etc) of human beings or animals. 

3.1.15 Medically Used Room — Room intended to be 
used for medical, dental or veterinary examination, 
treatment or monitoring of persons or animals. 

3.1.16 Minor Surgical Theatre — Room in which 
minor operations are performed on ambulant or non- 
ambulant patients, if necessary using anesthetics or 
analgesics. 

3.1.17 Operating Plaster Room — Room in which 
plaster of Paris or similar dressings are applied while 
anaesthesia is maintained. 

NOTE — Such a room belongs to the operating room group 
and is usually spatially connected to it. 

3.1.18 Operating Preparation Room — Room in which 



l) With or without additives. 



patients are prepared for an operation, for example, 
by administering anaesthetics. 

NOTE — Such a room belongs to the operating room group 
and is spatially connected to it. 

3.1.19 Operating Recovery Room — Room in which 
the patient under observation recovers from the 
influence of anesthesia. 

NOTE — Such a room is usually very close to the operating 
room group but not necessarily part of it. 

3.1.20 Operating Sterilization Room — Room in which 
utensils required for an operation are sterilized. 

NOTE — Such a room belongs to the operating room group 
and is spatially connected to it. 

3.1.21 Operating Theatre — Room in which surgical 
operations are performed. 

3.1.22 Operating Wash Room — Room in which 
medical staff at an operation can wash for disinfection 
purposes. 

NOTE — Such a room belongs to the operating room group 
and is spatially connected to it. 

3.1.23 Physiotherapy Room — Room in which patients 
are treated by physiotherapeutic methods. 

3.1.24 Radiological Diagnostic Room — Room 
intended for the use of ionizing radiation for display 
of internal structures of the body by means of 
radiography or fluoroscopy or by the use of radio-active 
isotopes or for other diagnostic purposes. 

3.1.25 Radiological Therapy Room — Room intended 
for the use of ionizing radiation to obtain therapeutic 
effects on the surface of the body or in internal organs 
by means of X-radiation, gamma radiation or 
corpuscular radiation or by the use of radio-active 
isotopes. 

3.1.26 Room Group — Group of medically used rooms 
linked with each other in their function, by their 
designated medical purpose or by interconnected 
medical electrical equipment. 

3.1.27 Urology Room — Room in which diagnostic or 
therapeutic procedures are performed on the urogenital 
tract using electromedical equipment, such as X-ray 
equipment, endoscopic equipment and high-frequency 
surgery equipment. 

3.1.28 Ward — Medically used room or room group 
in which patients are accommodated for the duration 
of their stay in a hospital, or in any other medical 
establishment. 

3.2 Zones of Risk (see also Annex A). 

3.2.1 Flammable Anaesthetic Atmosphere — Mixture 
of a flammable anaesthetic vapour and/or a vapour of 
a flammable disinfection or cleaning agent with air in 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



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such a concentration that ignition may occur under 
specified conditions. 

3.2.2 Flammable Anaesthetic Mixture — Mixture of a 
flammable anaesthetic vapour with oxygen or with 
nitrous oxide in such a concentration that ignition may 
occur under specified conditions. 

3.2.3 Zone G — Volume in a medically used room in 
which continuously or temporarily small quantities of 
flammable anaesthetic mixtures may be produced, guided 
or used including the surroundings of a completely or 
partly enclosed equipment or equipment part up to a 
distance of 5 cm from parts of the equipment enclosure 
where leakage may occur because such parts are: 

a) unprotected and liable to be broken, 
c) subject to a high rate of deterioration, or 
c) liable to inadvertent disconnection. 

Where the leakage occurs into another enclosure which 
is not sufficiently (naturally or forcedly) ventilated and 
enrichment of the leaking mixture may occur, such an 
enclosure and possibly the surroundings of it (subject 
to possible leakage) up to a distance of 5 cm from said 
enclosure or part of it is regarded as a Zone G. 

3.2.4 Zone M — Volume in a medically used room in 
which small quantities of flammable anaesthetic 
atmospheres of flammable anaesthetics with air may 
occur. A Zone M may be caused by leakage of a 
flammable anaesthetic mixture from a Zone G or by 
the application of flammable disinfection or cleaning 
agents. Where a Zone M is caused by leakage, it 
comprises the space surrounding the leakage area of a 
Zone G up to a distance of 25 cm from the leakage 
point. 

3.3 Special Terms 

3.3.1 Equipotential Bonding — Electrical connection 
intended to bring exposed conductive parts or 
extraneous conductive parts to the same or 
approximately the same potential. 

3.3.2 Essential Circuit — Circuit for supply of 
equipment which is kept in operation during power 
failure. 

NOTE — Provisions for supply of such circuit separately from 
the remainder of the electrical installation are present. 

3.3.3 Generator Set — Self-contained energy convenor 
including all essential components to supply electrical 
power (for example, engine driven generator). 

3.3.4 Hazard Current — Total current for a given set 
of connections in an isolated power system that would 
flow through a low impedance if it were connected 
between either — isolated conductor and earth. 



The following hazard currents are recognized: 

a) Total hazard current — Hazard current of an 
isolated system with all supplied equipment, 
including the line isolation monitor, 
connected. 

b) Fault hazard current — Hazard current of an 
isolated system with all supplied equipment, 
except the line isolation monitor, connected. 

c) Monitor hazard current — Hazard current of 
the line isolation monitor. 

NOTE — This current is expressed in milliamperes 
(mA). 

3.3.5 Insulation Impedance Monitoring Device — A 
device measuring the ac impedance at mains frequency 
from either of the conductors of an isolated circuit to 
earth and predicting the hazard current that will flow 
when an earth fault occurs and providing an alarm when 
a preset value of that current is exceeded. 

3.3.6 Insulation Monitoring Device — Instrument 
indicating the occurrence of an insulation fault from a 
live part of an isolated electrical supply system to the 
protective conductor of the installation concerned. 

3.3.7 Insulation, Resistance Monitoring Device — 
Instrument measuring the ohmic resistance between 
the monitored isolated circuit and earth providing an 
alarm when the value of this resistance becomes less 
than a given limit. 

3.3.8 Medical Isolating Transformer — Electrical 
equipment used in medical practice intended to supply 
isolated power to medical electrical equipment in order 
to minimize the likelihood of discontinuity of supply 
in case of a failure to earth in the isolated power source 
or in equipment connected to it. 

3.3.9 Medical Safety Extra-Low Voltage (MSELV) — 
Voltage not exceeding a nominal value of 25 V ac or 
up to and including 60 V dc or peak value at rated 
supply voltage on the transformer or converter between 
conductors is an earth-free circuit isolated from the 
supply mains by a medical safety extra-low voltage 
transformer or by a converter with separate windings. 

3.3.10 Operating Residual Current — Value of a 
residual current causing a protective device to operate 
under specified conditions. 

3.3.11 Patient Environment — Any area up to 1.5 m 
distance from the intended location of the patient in 
which intentional or unintentional contact between 
patient and equipment or some other person touching 
the equipment can occur (see Annex B). 

3.3.12 Touch Voltage — Voltage appearing, during an 
insulation fault, between simultaneously accessible 
parts. 



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4 CLASSIFICATION 

4.1 The electrical installations covered in this Section 
are those in buildings intended for the following purposes: 

a) Hospitals and sanatoria — This includes any 
building or group of buildings, which is used 
for housing treating persons suffering from 
physical limitations because of health, age, 
injury or disease. This also includes 
infirmaries, sanatoria and nursing homes. 

b) Custodial institutions — This includes any 
building or group of buildings which is used 
for the custody and care of persons, such as 
children (excluding schools), convalescents 
and the aged, for example, home for the aged 
and infirm, convalescent homes, orphanages, 
mental hospitals, etc. 

5 GENERAL CHARACTERISTICS OF 
MEDICAL ESTABLISHMENTS 

5.0 General guidelines on the assessment of 
characteristics of installations in buildings are given 
in Part 1/Section 8, of this Code. For the purpose of 
installations falling under the scope of this Section, 
the characteristics given below apply. 

5.1 Environment 

The following environmental factors shall apply to 
hospitals: 

Environment Characteristics Remarks 
(1) (2) (3) 

Presence of Probability of 

water presence of 

water is 

negligible 

The quantity or — 

nature of dust or 

foreign solid 

bodies is not 

significant 

The quantity and 

nature of 

corrosive or 

polluting 

substances is not 

significant 



Presence of 
foreign solid 
bodies 



Presence of 
corrosive or 
polluting 
substances 



Locations where 
some chemical 
products are 
handled (for 
example, 
laboratories in 
hospitals) will be 
categorized as in 
Part 1/Section 8 



Mechanical 

stresses 

Seismic effect 
and lighting 



Impact and 
vibration of low 
severity 



Depends on the 
location of the 
building 



5.2 Utilization 

The following aspects of utilization shall apply: 



Utilization 

a) 



Characteristics 
(2) 



Remarks 

(3) 



Capability of 
persons 



Contact of 
persons with 
earth potential 



Conditions of 
evacuation 
during 
emergency 



Nature of 
process fire or 
risk or stored 
materials 



Children in 
locations 
intended for 
their occupation 
Handicapped 



Persons 
adequately 
advised or 
supervised by 
skilled persons 
Persons do not in 
usual conditions 
make contact 
with extraneous 
conductive parts 
or stand on 
conducting 
surfaces 
Difficult 
conditions of 
evacuation 



Fire or risk 



Applies to 
child-care homes, 
orphanages, etc. 

Applies to 
hospitals in 
general, sanatoria, 
nursing homes, 
etc, where the 
occupants are not 
in command of all 
their physical and 
intellectual 
abilities 

Applies to areas 
such as building 
substations, 
operations and 
maintenance staff 



Applies in general 
to hospitals and 
similar buildings, 
irrespective of 
density of 
occupation 
Many locations in 
hospital buildings 
in general would 
fall under 
category BE 1 of 
no significant fire 
or explosion risk, 
specific locations 
like, operation 
theatre, casualty 
medicine store, 
X-Ray block fall 
under BE 2 and 
BE 3 

{see Part 1/Section 
8 of this Code) 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



227 



SP 30 : 2011 



6 SAFETY CONSIDERATIONS 

6.0 General 

6.0.1 In the context of this Section 'installation' means 
any combination of interconnected electrical 
equipment within a given space or location intended 
to supply power to electrical equipment used in medical 
practice. 

6.0.2 As such, some parts of the installation may be 
present in the patient's environment, where potential 
differences, that could lead to excessive currents 
through the patient, must be avoided. For this purpose 
a combination of earthing of equipment and potential 
equalization in the installation seems to provide the 
best solution. A disadvantage of such a system is that 
in the case of an insulation fault in circuits directly 
connected to supply mains, the fault current may cause 
a considerable voltage drop over the protective earth 
conductor of the relevant circuit. Since a reduction of 
such a voltage drop by the application of increased 
cross-sectional areas of protective conductors is usually 
impractical, available solutions are the reduction of the 
duration of fault currents to earth by special devices or 
the application of a power supply which is isolated 
from earth, 

6.0.3 Generally a power supply system including a 
separated protective conductor is required (TN-S- 
system). 

In addition the following provisions may be required, 
depending upon the nature of the examinations or 
treatments performed: 

a) Additional requirements concerning 
protective conductors and protective devices 
to restrict continuous voltage differences. 

b) Restriction of voltage differences by 
supplementary equipotential bonding. During 
the application of equipment with direct contact 
to the patient, as least a potential equalized zone 
around the patient shall be provided with a 
patient centre bonding bar to which the 
protective and functional earth conductors of 
the equipment are connected. All accessible 
extraneous conductive parts in the zone shall 
be connected to this potential equalization bar. 

c) Restriction of the potential equalization zone 
to the zone around one patient, meaning 
practically around one operation table or 
around one bed in an intensive care room. 

d) If more than one patient is present in an area, 
connection of the various potential 
equalization centres to a central potential 
equalization busbar, which should preferably 
be connected to the protective earth system 
of the power supply for the given area. 



In its completed form the equipotential 
bonding network may consist partly of fixed 
and permanently installed bonding and partly 
of a number of separate bondings which are 
made when the equipment is set up near the 
patient. The necessary terminals for these 
bonding connections should be present on 
equipment and in the installation. 

e) Restriction of the duration of transient voltage 
difference by the application of residual 
current operated protective devices (earth 
leakage circuit-breakers). 

f) Continuity of power supply to certain 
equipment in the case of a first insulation fault 
to earth and restriction of transient voltage 
differences by application of isolating 
transformers. 

g) Monitoring of a first insulation fault to earth 
in an IT-system (the secondary side of an 
isolating transformer) with sufficiently high 
impedance to earth. 

h) Prevention of ignitions and fire in rooms 
where flammable anesthetics or flammable 
cleaning or disinfection agents are used by 
ventilation, anti- static precautions and careful 
layout of the installation. 

j) Safety supply system for major parts of the 
hospital, usually a diesel-powered generator. 
Recommendations for essential circuits to be 
connected to it. 

k) Special safety supply system for critical 
equipment as life-supporting equipment and 
operating room lamps. 

The power supply is taken over by these 
devices in a short time. The device may 
consist of rechargeable batteries possibly 
combined with converters or special 
generating sets. 
m) Suppression of electromagnetic interference 
achieved by the layout of the building and wiring 
and provision of screening arrangements. 

Limits for magnetic fields of mains frequency 
are necessary for a number of sensitive 
measurements. 

6.1 Safety Provisions 

6.1.1 Safety measures are divided into a number of 
provisions as given in Table 1 . 

6.1.2 Provision P Q shall be applicable to all buildings 
containing medically used rooms. Provision P 1 shall 
be applicable for all medically used rooms. 

Other requirements of this Section, need not be 
complied with if: 



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SP 30 : 2011 



Table 1 Safety Provisions 
(Clause 6.1.1) 



SI 


Provisions 


No. 




(1) 


(2) 


i) 


Po 


ii) 


Px 



Principal Requirements 

(3) 



Installation Measures 

(4) 



iii) 



iv) 



Duration of touch voltages restricted to a safe limit 

As Po but additionally: Touch voltages in patient 
environment restricted to a safe limit 

As P] but additionally: Resistance between extraneous 
conductive parts and the protective conductor but bar of 
the room not exceeding 0.1Q. 

As P\ or P 2 but additionally: Potential difference 
between exposed conductive parts, extraneous 
conductive parts and the protective conductor bus bar 
not exceeding 10 mV in normal condition (see Note ) 

As Pi or P 2 . Additional protection against electric shock 
by limitation of disconnecting time 

Continuity of the mains supply maintained in case of a 
first insulation fault to earth and currents to earth 
restricted 

Reduction of fault currents and touch voltages in case 
of a fault in the basic insulation 

Prevention of dangerous touch voltages in normal 
condition and in single fault condition (see Note ) 

No interruption of the power supply of the essential 
circuits of the hospital for more than 15 s 

No interruption of the power supply of life-supporting 
equipment for more than 15 s 

No interruption of the power supply of the operating 
lamp for more than 0.5 s 

Prevention of explosions, fire and electrostatic charges 

No exercise interference from electric and magnetic 
fields 



NOTE — Normal condition means without any fault in the installation. 



v) 


Pa 


vi) 


Ps 


vii) 


Pe 


viii) 


Pi 


ix) 


Gi 


x) 


Ei 


xi) 


E 2 


xii) 


A 


xiii) 


I 



TN-S,TT or IT system 

Additional to P : Supply system with additional 
requirements for protective earthing, etc. 

Additional to P { : Supplementary equipotential 
bonding 

As P { or P 2 : Measurement necessary, corrective 
action possibly necessary 



Additional to P\ or P 2 : Residual current operated 
protective device 

Additional to P h P 2 or P 3 : Isolated supply system 
with isolation monitoring 

Additional P\ or P 2 : Medical isolating transformer 
supplying one individually piece of equipment 

Additional to P\ or P 2 : Supply with medical 
safety, extra low voltage 

Safety supply system 

Special safety supply system 

Special safety supply system for operating lamp 

Measures concerning explosion and fire hazards 
Layout of building and installation, screening 



a) a room is not intended for the use of medical 
electrical equipment, or 

b) patients do not come intentionally in contact 
with medical electrical equipment during 
diagnosis or treatment, or 

c) only medical electrical equipment is used which 
is internally powered or of protection Class II. 

The rooms mentioned under (a), (b) and (c) may be 
massage rooms, general wards, doctor's examining 
room (office, consulting room), where medical 
electrical equipment is not used. 

6.1.3 Guidance on the application of the provisions 
are given in Table 2. 

6.1.4 A typical example of an installation in a hospital 
is given in Annex C. 

7 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

7.0 Exchange of Information 

7.0.1 Proper coordination shall be ensured between the 



architect, building contractor and the electrical engineer 
or the various aspects of installation design. The 
necessary special features of installations shall be 
ascertained beforehand with reference to Table 2. 

7.1 Circuit Installation Measures for Safety 

Provisions — See Table 1, col 3. 

7.1.1 Provision P : General 

7.1.1.1 All buildings in the hospital area which contain 
medically used rooms shall have a TN-S, TT or IT 
power system. The conventional touch voltage limit 
(U L ) is fixed at 50 Vac. 

NOTE — The use of TN-C-S system (in which the PEN- 
conductor may carry current in normal condition) can cause 
safety hazards for the patients and interfere with the function 
of medical electrical equipment, data processing equipment, 
signal transmission lines, etc. 

7.1.2 Provision F, ; Medical TN-S System 

7.1.2.1 The conventional touch voltage limit (U L ) is 
fixed at 25 V ac. 

7.1.2.2 Protective conductors inside a medically used 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



229 



SP 30 : 2011 



Table 2 Examples of Application of Safety Provisions 

(Clause 6.1.3) 



SI Medically Used Room 
No. 






Protective Measures 




Safety Sup 
System 




Explosions 
and Fire 


Measures 

Against 
EM Fields 




*^~~ 










-**. 


/ — 






jP</Pi 


Pi 


^3 


Pa 


p s p* 


Pi. 


GE 


Ex 


E 2 


A 


/ 


(1) (2) 


(3) 


(4) 


(5) 


(6) 


(7) (8) 


(9) 


(10) 


(11) 


(12) 


(13) 


(14) 


i) Message room 


M 














X 










ii) Operating wash room 


M 


X 











X 










iii) Ward general 


M 














X 










iv) Delivery room 


M 


X 




X 


o 





X 


o 


X 








v) ECG, EEG, EMG room 


M 


X 




X 







X 








X 


vi) Endoscopic room 


M 


X 




X 




o 


X 




o 






vii) Examination or treatment room 


M 







X 


o 


o 


X 











viii) Labour room 


M 


X 




X 








X 











ix) Operating sterilization room 


M 


o 




X 




o 


X 










x) Urology room (not being an 
operating theatre) 


M 


X 




X 







X 











xi) Radiological diagnostic and 
therapy room, other than 
mentioned under SI No. (xx) and 
(xxiv) 


M 


X 




X 







X 










xii) Hydrotherapy room 


M 


X 




X 





o 


X 










xiii) Physiotherapy room 


M 


X 




X 








X 










xiv) Anaesthetic room 


M 


X 


X 


x t 


X 





X 


X 


X 


O 





xv) Operating theatre 


M 


X 


X 


x, 


X 





X 


X 


X 


X 


X 


xvi) Operating preparation room 


M 


X 


X 


Xi 


X 





X 


X 


X 


X 


X 


xvii) Operating plaster room 


M 


X 




X t 


X 





X 


X 


X 


X 


X 


xviii) Operating recovery room 


M 


X 


X 


X] 


X 





X 


X 


X 


X 


X 


xix) Outpatient operating theatre 


M 


X 




x, 


X 


o 


X 


X 


X 


X 


X 


xx) Heart catheterization room 


M 


X 


X 


X, 


X 


o 


X 


X 


X 




X 


xxi) Intensive care room 


M 


X 





Xj 


X 


o 


X 


X 


X 




X 


xxii) Intensive examination room 


M 


X 


o 


X! 


X 





X 


o 







X 


xxiii) Intensive monitoring room 


M 


X 





x, 


X 





X 


X 


X 




X 


xiv) Angiographic examination room 


M 


X 


o 


x, 


X 


o 


X 













xxv) Hemodialysis room 


M 


X 


X 


x, 


X 




X 










xxvi) Central monitoring room {see 
Note) 


M 


X 


o 


Xj 


X 


o 


X 








o 



NOTE — Only if such a room is part of a medical room group and therefore installed in the same way as an intensive monitoring room. 
Central monitoring room having no conductive connection to the medically used room (for example, by use of isolating coupling 
devices for signal transmission) may be installed as non-medically used room (provision P only). 

Explanation; M = Mandatory measure. 

X = Recommended measure. 

Xj = As X, but only for equipment described in 7.1.6.7. 

O = Additional measure, may be considered desirable. 



room shall be insulated: their insulation shall be 
coloured green-yellow (see Part l/Section4 of this 
Code). 

7.1.2.3 Exposed conductive parts of equipment being 
part of the electrical installation used in the same room 
shall be connected to a common protective conductor. 

7.1.2.4 A main equipotential bonding with a main 
earthing bar shall be provided near the main service 



entrance. Connections shall be made to the following 
parts by bonding conductors: 

a) lightning-conductor; 

b) earthing systems of the electric power 
distribution system; 

c) the central heating system; 

d) the conductive water supply line; 

e) the conductive parts of the waste water line; 



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NATIONAL ELECTRICAL CODE 



f) the conductive parts of the gas supply; and 

g) the structural metal framework of the building, 
if applicable. 

Main equipotential bonding conductors shall have 
cross-sectional areas not less than half the cross- 
sectional area of the largest protective conductor of 
the installation, subject to a minimum of 6 mm 2 . The 
cross-sectional area need not, however, exceed 25 mm 2 , 
if the bonding conductor is of copper or a cross- 
sectional area affording equivalent current-carrying 
capacity in other metals. 

7.1.2.5 Each medically used room or room group shall 
have its own protective conductor bus bar, which should 
have adequate mechanical and electrical properties and 
resistance against corrosion. 

This bus bar may be located in the relevant power 
distribution box. The leads connected to terminals of 
such a protective conductor bar shall be identified and 
shall be similarly designated on drawings of the 
installation system. 

7.1.2.6 The impedance (Z) between the protective 
conductor bar and each connected protective conductor 
contact in wall sockets or terminals should not exceed 
0.2 Q, if the rated current of the overcurrent protective 
device is 16 A or less. In case of a rated current 
exceeding 1 6 A the impedance should be calculated 
using the formula: 

25 

Z = Q in all cases Z shall not exceed 0.2 H. 

6.1, 

where 

7 r = rated current of overcurrent protective 

device in amperes (A). 

NOTE — The measurement of the protective conductor 
impedance should be performed with an ac current not less 
than 10 A and not exceeding 25 A from a source of current 
with a no-load voltage not exceeding 6 V, for a period of at 
least 5 s. 

7.1.2.7 The cross-sectional area of the protective 
conductor shall be not less than the appropriate value 
shown in Table 3. 

Table 3 Cross-sectional Area of Conductors 



SI 


Cross-sectional Area of 


Minimum Cross-sectional 


No. 


Phase Conductor, S, 


Area of the Corresponding 




mm 2 


Protective Conductor, PE, 

mm 2 


(1) 


(2) 


(3) 


i) 


S<16 


S 


ii) 


\6<S<35 


16 


iii) 


S>35 


sn 



NOTE — If the application of this table produces non- 
standard sizes, conductors having the nearest standard cross- 
sectional area are to be used. 



SP 30: 2011 

The values given in Table 3 are valid only if the 
protective conductor is made of the same metal as the 
phase conductors. If this is not so, the cross- sectional 
area of the protective conductor is to be determined in 
a manner which produces a conductance equivalent to 
that which results from the application of Table 3. 

The cross- sectional area of every protective conductor 
which does not form part of the supply cable or cable 
enclosure shall be, in any case, not less than: 

a) 2.5 mm 2 , if mechanical protection is provided, 
and 

b) 4 mm 2 , if mechanical protection is not 
provided. 

7.1.2.8 It may be necessary to run the protective 
conductor separate from the phase conductors, in order 
to avoid measuring problems when recording 
bioelectric potentials. 

7.1.3 Provision P 2 : Supplementary Equipotential 
Bonding 

7.1.3.1 In order to minimize the touch voltage, all 
extraneous conductive parts shall be connected to the 
system of protective conductors. 

An equipotential conductor bar shall be provided. It 
should be located near the protective conductor bar 
(see also 7.1.2.5). A combined protective conductor 
and equipotential bonding bar may be used, if all 
conductors are clearly marked according to 7.1.2.5 
and 7.1.3.3 (e). 

7.1.3.2 Connections shall be provided from the 
equipotential bonding bar to extraneous conductive 
parts, such as pipes for fresh water, heating, gases, 
vacuum and other parts with a conductive surface area 
larger than 0.02 m 2 or a linear dimension exceeding 
20 cm, or smaller parts that may be grasped by hand. 

Additionally the following requirements supply: 

a) Such connections need not be made to: 

1) Extraneous conductive parts inside of 
walls (for example structural metal frame 
work of buildings) having no direct 
connection to any accessible conductive 
part inside the room, and 

2) conductive parts in a non-conductive 
enclosure. 

b) In locations where the position of the patient 
can be predetermined this provision may be 
restricted to extraneous conductive parts 
within the patient environment (see 
Annex B) 

c) In operating theatres, intensive care rooms, 
heart catheterization rooms and rooms 



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intended for the recording of bioelectrical 
action potentials all parts should be connected 
to the equipotential bonding bar via direct and 
separate conductors. 

7.1.3.3 The following requirements shall be fulfilled: 

a) The impedance between extraneous 
conductive parts and the equipotential 
bonding bar shall not exceed 0.1. 

NOTE — The measurement of this impedance should 
be performed with a current not less than 10 A and not 
exceeding 25 A during not less than 5 s from a current 
source with a no-load potential not-exceeding 6 V ac. 

b) All equipotential bonding conductors shall be 
insulated, the insulation being coloured green/ 
yellow. 

NOTE — Insulation of the equipotential bonding 
conductors is necessary, to avoid loops by contact and 
to avoid picking up of stray currents. 

c) Equipotential conductors between 
permanently installed extraneous conductive 
parts and the equipotential bonding bar shall 
have a cross-sectional area of not less than 
4 mm 2 copper or copper equivalent. 

d) The equipotential bonding bar, if any, should 
have adequate mechanical and electrical 
properties, and resistance against corrosion. 

e) The conductors connected to the equipotential 
bonding bar shall be marked and shall be 
similarly designated on drawings of the 
installation system. 

f) A separate protective conductor bar and an 
equipotential bonding bar in a medically used 
room or in a room group shall be inter- 
connected with a conductor having a cross- 
sectional area of not less than 16 mm 2 copper 
or its equivalent (see also 7.1.3.1). 

g) An adequate number of equipotential bonding 
terminals other than those for protective 
conductor contacts or pins of socket outlets 
should be provided in each room for the 
connection of an additional protective 
conductor of equipment or for reasons of 
functional earthing of equipment. 

7.1.4 Provision P 3 : Restriction of Touch Voltage in 
Rooms Equipped for Direct Cardiac Application 

7.1.4.1 The continuous current through a resistance of 
1 000 connected between the equipotential bonding bar 
and any exposed conductive part as well as any 
extraneous conductive part in the patient environment 
shall not exceed 10 pA in normal condition for 
frequencies from dc to 1 kHz. 

For a description of patient environment, see Annex B. 



Where the measuring device has an impedance and a 
frequency characteristics as given in Annex D, the 
current may also be indicated as a continuous voltage 
with a limit of 10 mV between the parts mentioned 
above. 

a) During the test it is assumed that fixed and 
permanently installed medical electrical 
equipment is operating. 

b) 'Normal conditions' means 'without any fault 
in the installation and in the medical electrical 
equipment'. 

Compliance with this requirement may be achieved 
through one or more of the following methods: 

a) Extraneous conductive parts may be: 

1) connected to the equipotential bonding 
bar by a conductor of a large cross- 
sectional area in order to reduce the 
voltage drop across such a conductor, 

2) insulated so that it is not possible to touch 
them unintentionally, and 

3) provided with isolating joints at those 
places where they enter and leave the 
room. 

b) Exposed conductive parts of permanently 
installed equipment may be isolated from the 
conductive building construction. 

7.1.5 Provision P 4 : Application of Residual- Current 
Protective Devices 

7.1.5.1 The use of a residual-current protective device 
is not recognized as a sole means of protection and 
does not obviate the need to apply the provisions P l 
and P v 

7.1.5.2 Each room or each room group shall be 
provided with at least one residual-current protective 
device. 

7.1.5.3 A residual-current protective device shall have 
a standard rated operating residual-current / A < 30 mA. 

7.1.5.4 A medical isolating transformer and the circuits 
supplied from it shall not be protected by a residual- 
current protective device. 

7.1.5.5 Electrical equipment such as general lighting 
luminaries, installed more than 2.5 m above floor level 
need not be protected by a residual-current protective 
device. 

7.1.5.6 Fixed and permanently installed electromedical 
equipment with a power consumption requiring an 
overcurrent protective device of more than 63 A rated 
value may be connected to the supply mains by use of 
a residual-current protective device with / A < 300 mA. 



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7.1.6 Provision P 5 : Medical IT-System 

7.1.6.0 The use of a medical IT- system for the supply 
of medically used rooms for example operating 
theatres, may be desirable for different reasons: 

a) A medical IT-system increases the reliability 
of power supply in areas where an interruption 
of power supply may cause a hazard to patient 
or user; 

b) A medical IT-system reduces an earth fault 
current to a low value and thus also reduces 
the touch voltage across a protective 
conductor through which this earth fault 
current may flow; 

c) A medical IT-system reduces leakage currents 
of equipment to a low value, where the 
medical IT-system is approximately 
symmetrical to earth; 

It is necessary to keep the impedance to earth 
of the medical IT-system as high as possible. 
This may be achieved by: 

1) restriction of the physical dimensions of 
the medical isolating transformer, 

2) restriction of the system supplied by this 
transformer. 

3) restriction of the number of medical 
electrical equipment connected to such a 
system, and 

4) high internal impedance to earth of the 
insulation monitoring device connected 
to such a circuit. 

If the primary reason for the use of medical IT-system 
is the reliability of the power supply, it is not possible 
to define for such a system a hazard current and an 
insulation resistance monitoring device should be used. 

If on the other hand the restriction of leakage current 
of equipment is the main reason for the use of the 
medical IT-system, an insulation impedance 
monitoring device should be used. 

7.1.6.1 For each room or each room group at least one 
fixed and permanently installed medical isolating 
transformer shall be provided. 

7.1.6.2 A medical isolating transformer shall be 
protected against short circuit and overload. 

In case of a short circuit or a double earth fault in parts 
of opposite polarity of the medical IT-system the 
defective system shall be disconnected by the relevant 
overcurrent protective device. 

If more than one item of equipment can be connected 
to the same secondary winding of the transformer, at 
least two separately protected circuits should be 
provided for reasons of continuity of supply. 



7.1.6.3 Overcurrent protective devices shall be easily 
accessible and shall be marked to indicate the protected 
circuit. 

7.1.6.4 An insulation monitoring device shall be 
provided to indicate a fault of the insulation to earth of 
a live part of the medical IT-system. 

7.1.6.5 Fixed and permanently installed equipment 
with a rated power input of more than 5 kVA and all 
X-ray equipment (even with a rated power input of 
less than 5 kVA) shall be protected by provision P 4 . 
Electrical equipment such as general lighting, more 
than 2.5 m above floor level, may be connected directly 
to the supply mains. 

7.1.6.6 General requirements for insulation monitoring 
devices 

A separate insulation resistance or impedance 
monitoring device shall be provided for each secondary 
system. It shall comply with the requirements given 
below: 

a) It shall not be possible to render such a device 
inoperative by a switch. It shall indicate 
visibly and audibly if the resistance or 
impedance of the insulation falls below the 
value given in 7.1.6.7 and 7.1.6.8. 

The arrangement may be provided with a stop 
button for the audible indication only. 

b) A test button shall be provided to enable 
checking the response of the monitor to a fault 
condition as described in 7.1.6.4. 

c) The visible indication mentioned in (a) of the 
insulation monitoring device shall be visible 
in the monitored room or room group. 

d) The insulation monitoring device should be 
connected symmetrically to the secondary 
circuit of the transformer. 

7.1.6.7 Insulation resistance monitoring device 

The ac resistance of an insulation resistance monitoring 
device shall be at least 100 k. The measuring voltage 
of the monitoring device shall exceed 25 V dc, and the 
measuring current (in case of a short circuit of an 
external conductor to earth) shall not exceed 1 mA. 
The alarm shall operate if the resistance between the 
monitored isolated circuit and earth is 50 k or less, 
setting to a higher value is recommended. 

7.1.6.8 Insulation impedance monitoring device 

An insulation impedance monitoring device shall give 
readings calibrated in total hazard current with the 
value of 2 mA near the centre of the meter scale. 

The device shall not fail to alarm for total hazard 
currents in excess of 2 mA. In no case, however, shall 



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the alarm be activated until the fault hazard current 
exceeds 0.7 mA. 

During the checking of the response of the monitor to 
a fault condition the impedance between the medical 
IT-system and earth shall not decrease. 

NOTE — The values of 2 mA or 0.7 mA are based on practical 
experience with 1 10 to 120 V power supplies. For a 220-240 V 
power supply it may be necessary to increase these values to 
4 mA and 1.4 mA because of the higher leakage current 
of equipment. 

7.1.7 Provision P 6 : Medical Individual Electrical 
Separation 

7.1.7.0 Individual electrical separation of a circuit is 
intended to prevent shock currents through contact with 
exposed conductive parts which may be energized by 
a fault in the basic insulation. 

7.1.7.1 The source of supply shall be a medical isolating 
transformer. 

7.1.7.2 Only one item of equipment shall be connected 
to one source of supply. 

7.1.7 J The voltage of the secondary circuit shall not 
exceed 250 V. 

7.1.7.4 Live parts of the separated circuit shall not be 
connected at any point to any other circuit or to earth. 

7.1.7.5 To avoid the risk of a fault to earth, particular 
attention shall be paid to the insulation of such circuits 
from earth, especially for flexible cables and cords. 

7.1.7.6 Flexible cables and cords shall be visible 
throughout any part of their length where they are liable 
to mechanical damage. 

7.1.7.7 All conductors shall be physically separated 
from those of other circuits. 

7.1.8 Provision P 1 : Medical Safely Extra-Low Voltage 
(MSELV) 

7.1.8.1 Medical safety extra-low voltage shall not 
exceed 25 V ac or 60 V dc peak value. 

7.1.8.2 A supply transformer for medical safety extra- 
low voltage shall comply with relevant Indian 
Standards. 

7.1.8.3 A source of medical safety extra-low voltage 
other than a transformer shall have at least the same 
separation and insulation to other circuits and earth as 
required for the transformer under 7.1.8.2. 

7.1.8.4 Live pans at medical safety extra-low voltage 
shall not be connected to live parts or protective 
conductors forming part of other circuits or to earth. 

7.1.8.5 Exposed conductive parts shall not intentionally 
be connected to: 



a) earth, or 

b) protective conductors or exposed conductive 
parts of another system, or 

c) extraneous conductive parts except that, 
where electrical equipment is inherently 
required to be connected to extraneous 
conductive parts, it is ensured that those parts 
cannot attain a voltage exceeding medical 
safety extra-low voltage. 

7.1.8.6 Live parts of circuits at medical safety extra- 
low voltage shall be electrically separated from other 
circuits. Arrangements shall ensure electrical 
separation not less than required between the input and 
output of a medical safety extra-low voltage 
transformer. 

In particular, electrical separation not less than that 
provided between the input and output windings of a 
medical safety extra-low voltage transformer shall be 
provided between the live parts of electrical equipment 
such as relays, conductors, auxiliary switches and any 
part of a circuit with a higher voltage. 

7.1.8.7 Medical safety extra-low voltage circuit 
conductors shall either be physically separated from 
those of any other circuit or where this is impracticable, 
one of the following arrangements is required: 

a) Medical safety extra-low voltage circuit 
conductors shall be enclosed in a non-metallic 
sheath additional to their basic insulation. 

b) Conductors of circuits at different voltages 
shall be separated by an earthed metallic 
screen or an earthed metallic sheath. 

c) Where circuits at different voltages are 
contained in a multi-conductor cable or 
other grouping of conductors, medical 
safety extra-low voltage circuits shall be 
insulated, individually or collectively, for 
the highest voltage present. 

NOTE — In the above arrangements, basic-insulation 
of any conductor should comply only with the 
requirements for the voltage of the circuit of which it 
is a part. 

7.1.8.8 Plugs and socket-outlets shall comply with the 
following requirements: 

a) Supply systems of different voltages or 
different kinds or nature shall not have 
interchangeable plugs and sockets, and 

b) Socket-outlets shall not have a protective 
conductor contact. 

7.2 Wiring 

7.2.1 The general design of wiring shall conform to 
Part 1/Section 9 of this Code. 



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7.2.2 All panel boards and switchboards shall 
preferably be of dead front type, enclosed in metal 
cabinet. Where locked cabinets are provided, all locks 
should be keyed alike. Switchboard and panel boards 
shall be installed in non-hazardous locations. 

7.2.3 Circuit-breakers are preferred to switchfuse units 
in power and lighting feeders. 

7.2.4 Inside the wards only silent type wall mounted 
switches should be used to reduce noise. The lighting 
points shall be so grouped so that minimum lighting 
may be switched on during night time. 

7.2.5 Separate circuits shall be provided for X-ray, 
electrotherapy, diathermy, electrocardiograph, etc. 
Advice of equipment manufacturers shall also be 
sought in their installation. 

7.2.6 In corridors and spaces accessible to public 
provisions shall be made for lighted signs. 

7.2.7 Special convenience outlets in corridors spaced 
about 12 m apart are desirable for portable treatment 
equipment and cleaning machines. 

7.3 Feeders 

The general provisions laid down in Part 1 /Section 9 
of this Code shall apply. 

7.4 Service Lines 

7.4.1 The general provisions laid down in IS 8061 shall 
apply. 

7.4.2 The main supply conductors shall preferably be 
brought into the building underground to reduce the 
possibility of interruption of power supply. 

7.5 Building Substation 

7.5.0 General 

The design of power supply for hospital and similar 
buildings shall take into account the concentration of 
power demand for the various electrical loads. If the 
load demand is high requiring supply at high voltage, 
accommodation of substation equipment will be 
required. Emergency and standby power- supply needs 
of hospital buildings shall also be taken into account 
in designing the building substation. 

7.5.1 While calculating the power requirement, the 
diversity factor for different electrical appliances and 
installations shall be considered. For guidance, Table 4 
gives reference values of power requirement and 
diversity factor for the different parts in a hospital 
installation. 

7.5.2 The location and layout of building sub-station 
and emergency diesel generating set/s shall conform 
to the general rules laid down in Part 2 of this Code. 



Table 4 Power Requirement 

(Clause 7.5.1) 



SI No. 


Part of Electrical 


Proportion of 


Diversity 




Installation 


Total Power 
Requirement 

Percent 


Factor 


(1) 


(2) 


(3) 


(4) 


i) 


Lighting 


25 


0.9 


ii) 


Air-conditioning 


15 


1.0 


»i) 


Kitchen 


10 


0.6 


iv) 


Sterilizer 


10 


0.6 


v) 


Laundry 


5 


0.6 


vi) 


Lifts 


15 


1.0 


vii) 


Electromedical 
installations and 
other loads 


20 


0.6 



7.6 System Protection 

7.6.0 General 

The general rules for protection for safety laid down 
in Part 1 of this Code shall apply. Reference should 
be made to SP 7 for guidelines for fire-protection of 
buildings. The additional rules given below shall 
apply. 

7.6.1 The type of buildings covered in this Section fall 
under Group CI (hospitals and sanatoria), C2 (custodial 
institution), and C3 (panel institutions — - for mental 
hospitals, and similar buildings) from the fire-safety 
classification point of view. 

7.6.2 In hospitals and similar buildings, besides fire- 
fighting equipment manually operated electrical fire 
alarm system and automatic fire-alarm system shall 
be provided. Restricted paging system arrangement 
with sound alarm/indicators in the duty rooms/nurses 
rooms shall be made. 

7.6.3 For guidelines on selection of fire detectors, see 
SP 7. The wiring for fire-fighting systems shall be 
segregated from other wiring to reduce risk of damage 
to them in the case of fire. For high-rise buildings, the 
fire-fighting pump motors are generally large and they 
draw heavy current. Sufficient care shall be taken to 
ensure that the supply to such motors is maintained 
properly. 

7.7 Fire-protection 

Where electrical equipment contains pipes or tubes of 
combustion supporting gases, such as oxygen or nitrous 
oxide, the following additional requirements apply: 

a) Gas outlets shall be located at least 20 cm 
away from electrical components which, in 
normal use or in case of a fault, could generate 
sparks. 

b) The gas-flow shall not be directed towards 
such electrical components. 



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c) Electrical wiring shall only be allowed to be 
run in a common enclosure, for example in a 
common conduit for channel, with tubes for 
combustion supporting gases, such as oxygen 
or nitrous oxide, if in the relevant circuit the 
product of the no-load voltage in volts (V) 
and the short-circuit current in amperes (A) 
does not exceed 10. 

d) If the requirements in (c) cannot be. fulfilled 
gas-tight separation shall be provided between 
the electrical wiring and the tubes for gases. 
The gas-tight separation shall be electrically 
conducting and shall be connected to the 
protective earth busbar. 

e) Where electrical leads are close to a pipeline 
guiding ignitable gases or oxygen, a short- 
circuit of these leads or a short-circuit of one 
lead with a metal duct or pipeline shall not 
result in a temperature which may cause 
ignition. 

8 ADDITIONAL REQUIREMENTS FOR 
HAZARDOUS LOCATIONS IN HOSPITALS 

8.1 Provision A: Explosion and Fire Protection 

8.1.1 Explosion Protection: General 

a) When the administration of flammable 
anaesthetic atmospheres or flammable 
anesthetics or flammable cleaning and/or 
disinfection agents with air or oxygen and 
nitrous oxide is intended, special measures to 
avoid ignitions and fire are necessary. These 
measures include mainly the use of antistatic 
flooring. 

b) Effective ventilation and the application of a 
suction system on anaesthesia equipment 
assists in reducing flammable concentrations 
of flammable anaesthetic mixtures in the 
patient environment, the anaesthetists 
working-place and the operating table. The 
effectiveness of a ventilation, system may be 
subjected to National Regulations. 

c) Limits of zones of risk are given in Annex A. 
Zones of risk exist only when flammable 
anesthetics or flammable cleaning and/or 
disinfection agents are used. 

d) Requirements on construction, marking and 
documentation of medical electrical 
equipment of category AP or APG are given 
in IS 13450 (Parti). 

Allocation of equipment of the categories AP 
or AG to zones of risk in operating theatres 
or other anaesthetic rooms are under 
consideration. 



e) Mains plug connections, switches, power 
distribution boxes and similar devices, which 
may cause ignition shall be kept outside zones 
of risk. 

8.2 Antistatic Floor 

8.2.1 Antistatic floors shall be used in rooms where 
zones of risk occur. 

Where antistatic floors are used in conjunction with 
non-antistatic floors marking should be provided, 
which should be described in the application code. 

8.2.2 The resistance of an antistatic floor shall not 
exceed 25 MQ at any time during the lifetime of the 
floor when measured according to IS 7689. 

NOTE — The fact that during the lifetime of the floor the 
resistance may changes should be taken into consideration. The 
resistance of terrazzo floors increases, while that of PVC floors 
decreases with time. 

8.2.3 If floors of low resistance (< 50 k) are used. 
Provision P 4 and/or P 5 shall be used to effectively limit 
the effects of fault currents. 

9 BUILDING SERVICES 

9.1 Lighting 

9,1.1 The general rules laid down in Part 1/Section 1 1 
of this Code shall apply. The choice of lamps, lighting 
fittings and the general lighting design together with 
the power requirement shall be plane based on the 
recommended values of illumination and glare index 
given in Table 5 (see also SP 72). 

9.2 Heating, Ventilation and Air- Conditioning 

The provisions of Part 1 /Section 11 of this Code shall 
apply. Provision shall be made to maintain positive 
air pressure and induct increased quantity of fresh air 
to avoid entry of gases from one room to another. 

9.3 Lifts 

9.3.1 The general rules laid down in Part 1 /Section 1 1 
of this Code shall apply. However, the design of lifts 
in hospitals and similar buildings shall be made taking 
into account the criteria given Table 5. 

9.3.2 Dimensions 

The outline dimensions of hospitals lifts shall conform 
to those laid down in Table 3 of IS 14665 (Part 1). 

9.3.3 Occupant Load 

For the types of buildings covered in this Section, the 
occupant load expressed as gross area in m 2 per person, 
shall be 15. 



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Table 5 Recommended Values of Illumination 

and Limiting Glare Index 
(Clauses 9.1.1 and 9.3.1) 

S! Buildings Illumination Limiting 

No. Glare Index 

(1) (2) (3) (4) 



i) Hospitals 






a) Reception and waiting rooms 


150 


16 


b) Wards 






1) General 


100 


13 1 ' 


2) Beds 


150 




c) Operating theatres/Dental 






surgeries 






1) General 


300 


10 


2) Tables/chairs 


(Special 
lighting) 


— 


d) Laboratories 


300 


19 


e) Radiology department 


100 


— 


f) Casualty and outpatient 
department 


150 


16 


g) Stairs, corridors 


100 


___ 


h) Dispensaries 


300 


19 


ii) Doctor's Surgeries 






a) Consulting rooms 


150 


_ 


b) Corridors 


70 


— 


c) Sight testing (acuity) wall 
charts and near vision 


450 


— 


types 






iii) Laundries/Dry -cleaning Works 






a) Receiving, sorting, washing, 
drying 


200 


25 


b) Dry-cleaning, bulk machine 
work 


200 


25 


c) Ironing, pressing, mending, 
spotting, dispatch 


300 


25 


iv) Offices 


(see Part 3/Section 2 of this 
Code) 


v) Kitchens 


200 2) 


25 



l} Care shall be taken to screen all bright light and areas from 

view of patients in bed. 
2) Special local lighting required over kitchen equipment. 



9.3.4 Car Speed 








These shall be as follows: 








SI Type of Lift 


No 


'. of Floors Car Speed 


No. 




Served 


(m/sec) 


(1) (2) 




(3) 


(4) 


i) Hospital passenger 


} 


13-20 


Above 1.5 


lift 


4-5 


0.5 to 0.75 


ii) Hospital bed lifts 








a) Short travel lifts 


in 


— 


0.25 


small hospitals 








b) Normal 




— 


0.5 


c) Long travel lifts 


in 


— 


0.6-1.5 


general hospitals 









9.3.5 Position 

It is convenient to position the hospital passenger lifts 
near the staircases. Hospital bed lifts shall be situated 
conveniently near the ward and operating theatre 
entrances. There shall be sufficient space near the 
landing door for easy movement of stretcher/trolley. 

10 TESTING OF INSTALLATION 

10.1 The various tests on the installation shall be carried 
out as laid down in Part 1/Section 13 of this Code. 

10.2 The initial testing of the installation shall also 
include: 

a) Testing of the effectiveness of protective 
measures (provisions P to P t ); 

b) Testing of the resistance of protective 
conductors and of the equipotential bonding; 

c) Testing of the insulation resistance between 
live conductors and earth in each separately 
fused circuit; 

d) Testing of the resistance of antistatic floors; 

e) Testing of the general safety supply system 
and 

f) Testing of the special safety supply system. 

11 STANDBY, SAFETY AND SPECIAL SAFETY 
SUPPLY SYSTEM 



11.1 Provision GE 

System 



Standby and Safety Supply 



11.1.1 Electrical systems for medical establishments 
shall comprise essential circuits capable of supplying 
a limited amount of lighting and power service which 
is considered essential for safety, life support and basic 
hospital operation during the time the normal electrical 
service is interrupted (see also Annex E). 

11.1.2 All medical establishments containing life- 
supporting equipment shall be provided with a safety 
supply system. 

11.1.3 Essential circuits shall provide facilities for 
charging batteries of a special safety supply system. 

11.1.4 Operation of a safety supply system shall not 
impair the function of protective measures. 

11.1.5 All parts of essential circuits shall be marked. 

11.1.6 An example of safety supply systems of a 
hospital is given in Annex F. 

11.1.7 A safety supply system shall be capable of 
automatically taking over the load of essential circuits 
in the event of a failure of the normal power supply. 

11.1.8 The taking-over procedure shall not start earlier 
than after a period of 2 s has elapsed during which the 



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system voltage has dropped below 90 V of the nominal 
value and shall be completed within 15 s after the 
starting of the taking-over procedure. 

Return to normal power supply should be delayed. For 
diesel- generators the delay should be at least 30 min. 

11,1.9 To prevent simultaneous damage, the main 
feeders for the safety supply system shall be segregated 
from the normal system wherever possible. 

11.2 Provisions E x and E 2 t Special Safety Supply 
System 

11.2.1 Provision E{. Special Safety Supply System, 
Medium Break 

11.2.1.1 A special safety supply system shall 
automatically take over the load within 15 s after a 
failure of the power supply at the medical establishment 
containing life- supporting equipment. 

11.2.1.2 It shall be possible to resume operation of 
equipment for maintaining important body functions, 
in particular breathing equipment, or equipment for 
resuscitation, within 15 s and to maintain operation 
for a period of 3 h subsequently, for example, via a 
battery with inverter or via a motor driven generator. 

11.2.1.3 Where the rating of the special safety supply 
system is sufficient the circuits of a medical IT-sy stem 
according to 7.1.6 may be connected to it. 

11.2.1.4 Where not all socket outlets in a medically 
used room are connected to the special safety supply 
system the connected socket outlets shall be marked 
clearly as such. 

11.2.2 Provision E 2 : Special Safely Supply System, 
Short Break 

11.2.2.1 A special safety supply system shall 
automatically take over the load within 0.5 s after a 
failure of the power supply at the operating lamp. 

11.2.2.2 Operation of at least one operating lamp shall 
be resumed after a switchover time not exceeding 0.5 s 
and operation shall be maintained for at least 3 h. 

11.2.3 Common Recommendations for the Provisions 
E ] and E 2 

11.2.3.1 The rated power of the source of a special 
safety supply system shall not be less than required by 
the connected functions. At least the loads which 
require continuity of supply shall be connected to the 
special supply system. 

11.2.3.2 Operation of a special safety supply system 
shall not impair the function of protective measures. 

For diesel-generators the requirements of 11,1.8 shall 
apply. 



11.2.3.3 Voltage deviations under normal conditions 
shall be less than 10 percent for periods of time 
exceeding 5s. 

11.2.3.4 Frequency deviations shall be less than 
1 percent for periods of time exceeding 5 s. 

11.2.3.5 The special safety supply system source shall 
be located outside the medically used rooms, if possible 
close to the relevant distribution point, so that physical 
damage to the cables connecting the source to the 
distribution point is unlikely. 

11.2.3.6 Operation of the special safety supply system 
shall be indicated by visual means in all rooms 
concerned. 

NOTE — It is recommended to provide additionally a total 
load indicator in each room connected to the same special safety 
supply system. 

11.2.3.7 Automatic means shall be provided to keep 
batteries optimally charged. 

11.2.3.8 The charging device shall be designed so that, 
starting from the fully charged conditions, it is possible 
to discharge continuously during 3 h at nominal output, 
and subsequently to re-change during 6 h after which 
it shall be possible to discharge once more for 3 h under 
the conditions mentioned above. 

11.2.3.9 It shall be possible to supply the charging 
circuit of a special safety supply system from the safety 
supply system, so that the special safety supply system 
batteries can be charged even during a failure of the 
normal power supply. 

12 MEASURES AGAINST INTERFERENCE 

PROVISION! 

12.1 Measures Against ac Interference 

12.1.1 In rooms where measurements of bioelectric 
potentials are performed measures against interference 
in the room and in the surrounding area should be 
affected, if such interference may cause incorrect 
measurements. Such rooms are: 

a) rooms intended for measurement of bio- 
electric potentials (EEG, ECG, etc); 

b) intensive examination rooms; 

c) intensive care and monitoring rooms; 

d) catheterization rooms; 

e) angiographic examination rooms; and 

f) operating theatres. 

12.2 Measures Against Interference Caused by 
Mains-Induced Electric Fields 

12.2.1 The electrical wiring on both sides of or inside 
walls, floor and ceiling of the rooms concerned should 



238 



NATIONAL ELECTRICAL CODE 



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be screened by means of metal shielding of cables or 
by metal conduits for cables and wiring. 

If such metal shielding is applied it should be connected 
to protective earth at one point only. 

12.2o2 Metal enclosures or pans of enclosures of fixed 
and permanently installed electrical equipment of 
Class II and III (such as of lighting fittings) should be 
connected to the equipotential bonding system. 

12.23 Where adequate measures according to 11.1 
cannot be applied and ECG and EEG monitoring is to 
be undertaken, it is recommended to shield the room 
or a part of the room against electric fields by installing 
a room screening within the wall structure. 

12.3 Measures Against Interference Caused by 
Mains-Induced Magnetic Fields 

12.3.1 It is recommended to provide sufficient distance 
between electrical components and equipment which 
may, cause magnetic interference and the place for the 
examination of patients. In practice the following 
values of magnetic field strength have been found to 
be sufficiently low to avoid magnetic interference: 

a) 4 x 10 7 T pp for ECG recording, and 

b) 2 x 10 7 T pp for EEG recording. 

NOTE — Ballasts incorporated in fluorescent lamp fittings 
generate an alternating magnetic field; those on the ceiling of 
the room immediately below the examination room are the ones 
most likely to cause interference. In some cases it may be 
necessary to remove ballasts of a certain type from the lighting 
fitting and to mount them at sufficient distance. 

12.3.2 Sufficient distance should be provided when 
installing units with strong stray magnetic fields such 
as transformers and motors. This applies also to the 
isolating transformer of provision P 5 . The distance 
should be 3 m or more. 

12.3.3 The rooms listed in 12.1 should not have large 
power cables passing through or adjacent to them. 
Suggested minimum distances are: 



Conductor Cross- 
Sectional Area 

10 to 70 
95 to 185 

240 



Distance, Min 
m 

3 

6 

>9 



NOTES 

1 Cables, either single phase or three phase, will have a 
negligible external field if the load is correctly distributed 
between phase or between phase and neutral but in practice 
faults between neutral and earth or incorrectly distributed loads 
between lines and neutral, and leakage currents will cause 
alternating magnetic fields in the vicinity of power cables. 

2 The values apply only to twisted cables. When bar systems 
or separated single cables are used, the distances may have to 
be substantially larger. 



12.4 Measures Against Interference from Radio 
Frequency Electromagnetic Fields 

12.4.0 Powerful radio frequency fields may cause 
interference in sensitive electromedical equipment. 

12.4.1 Normally such fields exist only where short-wave 
diathermy or surgical diathermy equipment is used and 
close to transmitting aerials used for such purposes as 
staff location and ambulance communications. The 
simplest measure against such interference is to locate 
equipment which causes it well away from areas where 
sensitive equipment is used. Additional measures are 
the inclusion of radio frequency rejection circuits in 
sensitive equipment and the use of short-wave diathermy 
equipment with a low modulation factor. 

If the measures described here are not sufficiently 
effective it may be necessary to use sensitive equipment 
with a screened room. 

NOTE — The construction of such a screened room should be 
entrusted to a specialist. An attenuation of 40 dB over the 
frequency range 150 kHz to 30 MHz is considered to be 
adequate. 

12.5 Electric Heating Cables 

12.5.0 The following requirement applies to electric 
heating cables embedded in or attached to surfaces in 
buildings. It does not apply to removable appliances 
which may be mounted on the surface of walls. 

12.5.1 Electric heating cables of any type should not 
be used in rooms where bioelectric potentials are 
recorded. 

NOTE — Due to the construction of such heating cables it is 
very likely, that the electric and magnetic fields will interfere 
with the recording of bioelectric potentials. Appropriate 
measures according to 12.2 and 12.3 should be taken. 

13 MISCELLANEOUS PROVISIONS 

13.1 Call Systems 

13.1.0 Electrical call and signal system when provided 
in hospitals should comply with the requirements given 
in 13.1.1 to 13.1.4.1 The following are the important 
call and signal system: 



a) Nurses call, 

b) Doctors' paging, and 

c) In-and-out register. 



NOTE — It is recommended that electrical call and signal 
system should be provided in all hospitals so that patients may 
receive prompt service and the doctors, nurses and attendants 
may work more efficiently. 

13.1.1 Nurses' Call System 

The nurses call system should be a wired electrical 
system whereby patients may signal for a nurse from 
the bed site. Two types of systems are recommended: 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



239 



SP 30 : 2011 



a) A simple one-way signal system which con- 
nects the bed side call stations with a signal 
at the nurses' station, utility room and floor 
pantry of the nursing unit. It simultaneously 
lights a dome light over the door of the room 
from which the call originated. The signal at 
the nurses' station may be in the form of an 
annunciator with a buzzer or a single light 
with a buzzer. Two or more lights in the ceiling 
of the corridor at the nurses' station to indicate 
the direction from which the call came are 
desirable for the latter arrangement. 

b) A central control panel should be set up pre- 
ferably on the ground floor incorporating a 
set of indicating panels according to the 
number of wards. Each indicating panel 
should have a number of small lamps 
according to the number of beds. At each bed 
there could be 4 push buttons. First for 
'Calling Nurses', second for 'Nurse Present', 
third for 'Setting Combination' and fourth for 
'Call for Doctor'. When any patient presses 
the push button the indication is at the central 
control room from where intimation to nurses 
can be sent. After reaching the bed site the 
nurse presses the 'Nurse Present' button which 
gives an indication to operator at the central 
control panel that the nurse is available near 
the particular bed. After attending the patient, 
the nurse presses the resetting button which 
puts the whole equipment to the original 
condition. If the patient needs further help of 
a doctor then the nurse again presses the fourth 
push button and the central control panel 
operator sends message to the doctor for that 
particular bed. 

13.1.1.1 For emergency call of nurse by the patient 
when he/she is inside a bath or water-closet, suitable 
pull cord switches shall be provided inside bath and 
water-closet. These switches when operating will give 
an indication at the central control panel from where 
intimation to nurse can be sent. 

13.1.1.2 Nurses call system may also be of the 
intercommunicating type with a microphone and 
loudspeaker at the bed connected to the nurses' station. 
The patient can signal for a nurse or speak to her and 
receive an answer. For maximum benefit and service, 
this system should include all the features described 
in 13.1.1 for the one-way signal system in addition to 
the inter-communicating features. 

13.1.2 Doctors Paging System 

This may consist of loudspeakers located throughout 
the hospital, clinics on which doctors' numbers can be 



sounded or the flasher type which indicates the doctors' 
numbers. The loudspeaker and other audible calls 
should not be used as they may disturb the patients 
and attendants. The flasher system consists of a 
keyboard and flasher at the telephone switchboard. The 
telephone operator may set the board to flash as many 
as three doctors' numbers automatically in rotation. 
The numbers appear on annunciators located in all 
sections of the corridors. The same number of 
numerals, at least three, should be used for each doctor 
so that a burnt out lamp may be located. 

13,1.2.1 These paging systems could be used for calling 
interns, administrators, heads of departments and their 
assistants and engineers. These flashers may also be 
used for other general calls such as 'fire' with a red 'F' 
and buzzer. The flasher call system has its shortcomings 
as the individual may fail to see the numbers when 
flashed. For this reason the flasher system should be 
supplemented with loudspeakers at points where 
interns, heads of departments and doctors may 
congregate, that is, in doctors' lounge, staff dining 
room, laboratory and engineers' office and such other 
areas where the calls may not disturb the patients. 

13.1.3 VHF Paging System 

This system consists of a low powered transmitting 
station from which calls are broadcast throughout the 
hospital to miniature receiving sets which the doctors 
and others may carry in their pockets. 

13.1.4 In-and-Out Register 

The doctors' in-and-out register permits the doctor to 
register 'IN' and 'OUT' with the minimum of effort 
and delay. The register consists of a board, at one or 
more entrances, on which all staff doctor, upon entering 
or leaving, operates a switch opposite his name which 
indicates whether or not he is in the building. The 
switch controls a light at or back of the name on all 
boards connected in the system. 

13.1.4.1 Except in very small hospitals, it is 
recommended to install register system with a board 
at two or more entrances and at the telephone 
switchboard. Such a system should include a recall 
feature which consists of a flasher unit, having a motor 
driven interrupter. This flasher unit, controlled at the 
telephone switchboard, will actuate a flashing light at 
the doctors' name on all register boards which indicates 
there is a massage for the doctors, and attracts the 
attention of doctor upon entering or leaving the 
building. Call back systems are used for nurses' and 
interns' bedrooms. With such system the nurses and 
interns can be awakened, called for duty, or called to 
the telephone by push-buttons in the office which 
operate buzzers in the rooms. The room called can 



240 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



answer by pushing a button which registers on an 
annunciator in the office. The main office buzzers may 
be connected through a selector switch so that serial 
rooms or sections may be called by one button. 

13.2 Telephones 

13.2 .0 A centralized EPABX System with adequate 
number of P&T lines shall be installed for internal and 
external communication. Interconnecting telephones 
should be provided for each important department and 
at patients' bed. These shall be interconnected to permit 
internal communication without operator's assistance. 
Facility shall be provided for external communication 
with these departments through operator's assistance. 
Some of the most important departments shall have 
direct access facility for external communication. At all 
special and important beds, telephone jacks should be 
installed so that a telephone may be plugged in any time. 

13.2.1 In case of operation theatre and rooms where 
surgical operations and dressing is done, concealed 
wiring should be provided to avoid risk of 
contamination. In other places, any type of general 
wiring may be acceptable. 

13.2.2 The concealed wiring and switch-socket outlets 
in the operation theatres shall be kept at a minimum 



height of 1.5 m from the floor as anaesthetic gases are 
heavier than air and gravitate to the floor. 

13.3 Clocks 

Electric clock system when provided, should have 
clocks at nurses' stations, main lobby, telephone 
switchboard, kitchen, laundry, dining room and boiler 
room, as well as in the operating and delivery rooms. 
The clocks should be of the recessed type, preferably 
with a narrow frame. Clocks in operating and delivery 
rooms should have sweep second hands. The general 
guidance provided in Part 1 /Section 11 of this Code 
shall apply. 

13.4 Other Special Installations 

The list of other special circuits in installations in 
hospitals are given below: 



a) 

b) 

c) 



d) 



Closed-circuit television in surgery depart- 
ment (for teaching purposes); 
Television sets in wards; 
Short-wave, ultraviolet rays or sterile ray 
lamps in ceilings of operating and delivery 
rooms around the operating light, to reduce 
the bacteria count; and 
Luminous signs. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



241 



SP 30: 2011 

ANNEX A 
{Clauses 3.2 and 8.1.1) 

ZONES OF RISK IN THE OPERATING THEATRE WHEN USING FLAMMABLE ANAESTHETIC 
MIXTURES OF ANAESTHETIC GASES AND CLEANING AGENTS 




cc 



ZONE G 



ZONE M 



Legend 



1 = Ventilation system 

2 - Ceiling outlet with sockets for electric power gases 

(for example, oxygen), vacuum and exhaust 
ventilation system for medical electrical equipment 

3 = Operation lamp 
4= Equipment 

5 = Operating table 



Legend 

6 = Foot switch 

7 = Additional zone M due to use of flammable 

disinfection and/or cleaning agents 

8 = Anaesthesia apparatus 

9 = Exhaust system for anaesthesia gases 

10 = Exhaust ventilation system 

1 1 = Parts unprotected and likely to the broken 



242 



NATIONAL ELECTRICAL CODE 



ANNEX B 

[Clauses 3.3.11, 7.1.3.2(b) and! A A] 

PATIENT ENVIRONMENT 



SP 30 : 2011 



/ m 



© ©\ 



£ 

m 






/" 



/ 




fT) OPERATION TABLE 

(7) MEDICAL ELECTRICAL 
^^ EQUIPMENT 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



243 



SP 30: 2011 



ANNEX C 
(Clause 6,1 A) 

EXAMPLE OF AN ELECTRICAL INSTALLATION IN A MEDICAL ESTABLISHMENT 




Legend 

1 = Heating pipes 

2 = Water supply 

3 = Gas supply 

4 = Distribution board 

5 = General ward 

6 = Hospital bed 

7 = Heating and water pipes 

8 = Medical IT-system for Operation Theatre 

9 = Insulation monitoring device 

10 = Medical isolating transformer 

11 - Socket outlet 

12 - Main distribution board. 



Legend 

13 = Main earthing bar 

14 = Joint 

15 = Water meter 

16 = Gas meter 

17 = Waste water 

18 = Earth electrode 

19 = Lighting protective system 

20 = From public electric power system 

L v L 2 , L 3 = phase conductors 
N - neutral conductors 
EC = bonding conductor 
PE = protective conductor 



244 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 

ANNEX D 
(Clause 7*1.4.1) 

SCHEMATIC PRESENTATION OF PROTECTIVE CONDUCTORS AND EQUIPOTENTIAL 

BONDING IN OPERATING THEATRES 




Legend 

1 = Feeder from the main service entrance 

(main distribution board) 

2 = Distribution of the floor 

3 = Operating theatre distribution panel 

4 = Safety supply system 

5 = Medical isolating transformer 

6 = Insulation monitoring device 

7 = Special safety supply system, E 2 

8 - Special safety supply system E, 

9 = Central heating 

10 = Metal window-frame 

1 1 = Metal cabinet for instruments 

12 = Meal washing-basin and water supply 

13 = Ceiling stand with outlets for gas supply 

14 = Ceiling stand with mains socket outlets 

(with terminals for equipotential bonding, 
enclosure connected to the protective 
conductor bar) 

15 = Alarm device for the insulation monitoring 

device (example) 

16 = Operating table (electrically driven) 



Legend 

17 = Operating lamp 

18 = Ampere meter for special safety 

supply system 

19 = X-ray equipment 

20 = Sterilizer 

21 = Residual-current protective device 

22 = Protective conductor bar 

23 = Equipotential conductor bar 

24 = Terminals for equipotential bonding 

25 = Operation 

26 = Warning 

27 = Green 

28 = Red 

29 = Buzzer 

30 = Stop button for buzzer 

31 = Test button 

PE = protective conductor 
EC = equipotential bonding 
L v L 2 , L 3 = phase conductors 
N = neutral conductor 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



245 



SP 30: 2011 



ANNEX E 
(Clause 11.1.1) 

SAFETY SUPPLY SYSTEM 



E-0 GENERAL 

E-0.1 This Annex contains recommendations for the 
design of the safety supply system in medical 
establishments. 

Priority is given to all aspects ensuring safe working 
conditions in medically used rooms. 

Interruption of normal electrical service in medical 
establishments may cause hazardous situations. 
Therefore, it is necessary to provide for continuity of 
power supply for vital services at all times. 

In some medically used rooms a special safety supply 
system should be provided additionally. It supplies life 
supporting equipment and the operating table lighting 
for 3 h only, that is, for a relatively short time if the 
mains supply or the safety supply system fails or the 
switch-over time cannot be tolerated. 

The safety supply system is intended to supply 
electrical energy for a longer period of time to essential 
circuits of the medical establishment if the mains 
supply fails by external causes. 

E-l ESSENTIAL SERVICES — LIGHTING 

E-l.l Essential lighting requirements will vary 
considerably in different locations, depending on the 
importance and nature of the work. In some instances, 
for example, operating table lighting in operating 
suites, and the critical working areas in the delivery 
room and recovery rooms, the degree and quality of 
emergency lighting should be approximately equal to 
that of the normal lighting. Even in these areas, 
however, considerable reduction in the general lighting 
may be acceptable. Ample socket-outlets connected to 
essential circuits should be available to enable portable 
lighting fittings to be used for any tasks outside the 
critical working area-which require a higher standard 
of lighting. 

E-1.2 No general recommendations can be made for 
the emergency lighting arrangements for stairs and 
corridors as needs will differ considerably according 
to the design and size of the hospital. As a general 
guide, safety lighting should be provided to enable 
essential movement of staff and patients to be carried 
out in reasonable safety. Safety lighting should also 
be provided in public waiting spaces, at entrances and 
exits, and in corridors used by members of the public, 
ambulance staff, etc. External emergency lighting will 



normally be restricted to the accident and emergency 
entrance areas. 

E-l. 3 Three grades of emergency lighting are 
suggested, namely: 

a) Grade A lighting of intensity and quality equal 
or nearly equal to that provided under normal 
supply conditions; 

b) Grade B reduced standard of lighting, for 
example, about half the normal standard, 
sufficient to enable essential activities to be 
properly carried out; and 

c) Grade C safety lighting of a much reduced 
standard but sufficient to allow the free 
movement of persons, trolleys, etc. 

Levels for Grades A, B and C are under consideration. 

E-1.4 Table 6 is intended as a general guide. Emergency 
lighting may be needed in areas not mentioned in the 
table. 

E-2 ESSENTIAL CIRCUITS — SOCKET- 
OUTLETS 

E-2.1 Socket-outlets should be so distributed that in 
each area where essential equipment will be used, 
socket-outlets connected to at least two separate sub- 
circuits are available. 

Table 7 is intended as a general guide. 

E-2. 2 Socket outlets in operating rooms for the 
connection of X-ray equipment for fluoroscopy should 
be supplied from an essential circuit. 

E-2.3 Electrical services, including automatic controls, 
which are essential for the safe operation of sterilizing 
equipment in operating theatre and the central sterile 
supply department should be supplied from an essential 
circuit. 

E-2.4 Blood banks and other clinical refrigerators are 
usually equipped with temperature retaining facilities 
which will satisfactorily safeguard against power 
failures of several hours' duration. Nevertheless, they 
shall be supplied from an essential circuit. 

E-2.5 Motors of surgical suction plant should be 
connected to an essential circuit. It is desirable that 
the motors should be so arranged that once they are 
switched on they will restart automatically, following 
an interruption of supply. 



246 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



Table 6 Emergency Lighting 

(Clause "EA A) 



Table 6 — (Concluded) 



SI 


Department or 


Area 


Grade of 


No. 


Location 




Lighting 


(1) 


(2) 


(3) 


(4) 


i) 


Major Operating 
Suites 








Operating theatre 


Critical working area 


Grade A 




Operating theatre 


General working area 


Grade B 




Anaesthetic rooms 


General working area 


Grade A 




Post operative 


General working area 


Grade A 




Intensive care room 


Circulating areas 


Grade C 


ii) 


Delivery Suites 










Critical working area 


Grade A 




Delivery rooms 


Other nursing areas 


Grade B 






Circulating areas 


Grade C 


iii) 


Accident and 

Emergency 

Departments 








Operating theatres 


Critical working area 


Grade A 




Intensive care rooms 


Critical working area 


Grade A 






General working area 


Grade B 






Circulating areas 


Grade C 


iv) 


Out-Patient 
Department 








Operating theatres 


Critical working area 


Grade A 




Treatment rooms 


General working areas 


Grade B 




Consulting rooms 


General working areas 


Grade B 






Circulating areas 


Grade C 




Pathological 


Essential working areas 


Grade B 




department 










Blood bank 


Grade A 






Transfusion laboratory 


Grade A 




Diagnostic X-ray 


General working area 


Grade B 




department 


(where portable X-ray 
machines may be used) 








Circulation areas 


Grade C 




Radiotherapy 


Treatment areas 


Grade A 




department 


Public circulating areas 


Grade C 




Pharmacy 


Dispensing areas 


Grade B 






Laboratory 


Grade B 


v) 


Ward Areas 








Intensive therapy 


Intensive nursing area 


Grade A 




units 


Other nursing areas 


Grade B 






Nurses' station or duty 


Grade B 






room 




vi) 


Special Baby Care 
Units 








Nurseries 


General working area 


Grade B 




Psychiatric wards 


General working area 


Grade B 




Treatment rooms 


General working area 


Grade A 




Other nursing areas 


General working area 


Grade C 
(night- 
lighting) 


vii) 


Central Sterile Supply General working area 


Grade B 




Department 






iii) 


Telephone Exchanges 


Essential working area 


Grade B 


ix) 


Operators Room 




Grade B 


x) 


Lifts 








Lifts cars 




Grade A 




Entrance and exit of 




Grade A 




elevators 






xi) 


General circulating 
Areas 








Public entrances and 


— 


Grade C 




exits 








Corridors and 


— 


Grade C 



SI Department or 
No. Location 

(1) (2) 



Area 



(3) 



Grade of 
Lighting 

(4) 



Corridors and — 


Grade C 


circulating spaces of 




deep planned designs 




ii) Assembly Areas 




Assembly rooms and — 


Grade C 


associated exists 




Public waiting space - — 


Grade C 


Plant rooms housing Working area 


Grade B 


essential plant 




Kitchens Essential working areas 


Grade B 



Table 7 Socket-Outlets in Essential Circuits 
(Clause E-2.1) 



SI 


Department 


Number of Socket- 


No. 




Outlets Connected to 

Essential Circuits (see 

Note) 


(1) 


(2) 


(3) 



i) Operating suits 
ii) Intensive care room and 
operating rooms in accident 
and emergency department 
iii) Delivery rooms 
iv) Post-anaesthetic recovery 

rooms 
v) Intensive therapy units 
vi) Radiological diagnostic room 
vii) Ward accommodation set aside 
for patents dependent on 
electrically driven equipment, 
for example, respirators, 
rocking beds, artificial kidney 
machines, etc. 
viii) Special baby care units 
ix) Pathology laboratories 
x) Wards where essential 
equipment such as suction 
apparatus will be used 



All 
All 



All 
All 

All 
All 
All 



All 

2 



staircases forming 
recognized means of 
escape 



2 sockets outlets for wards 
containing 1 to 4 beds and, 
pro rata, where the number 
of beds exceeds 4. 

NOTE — It is reasonable to assume that only essential 
equipment will be used in these areas during periods of power 
failure. The recommendation that all socket are connected to 
the Essential Circuits provide the most convenient choice of 
sockets outlets at any time, and to simplify installation. 



E-2.6 Safety supply systems for facilities for ventilation 
and air-conditioning purposes will usually apply only 
to plants which serve areas which are entirely 
dependent on mechanical ventilation and have no 
facilities for natural ventilation or where mechanical 
ventilation services are essential for clinical reasons. 
Where ventilation requirements are met by duplicate 
plants it will usually only be necessary for one of the 
plants to be supplied from the emergency source, thus 
ensuring air supplies of approximately 50 percent of 
the normal rate. Changeover switches, however, should 
be provided, to enable either of the plants to be 
connected to the emergency service. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



247 



SP 30: 2011 



E-2.7 Any mains-energized alarm and control circuits 
should be so arranged that they are automatically 
connected to the safety supply system in the event of a 
power failure. 

E-2.8 In biochemical laboratories and in the pharmacy 
about 50 percent of the normal load should be supplied 
from essential circuits. 

E-3 PARTS OF ESSENTIAL CIRCUITS 

E-3.1 Deep-freeze refrigerators and food storage 
refrigerators will normally operate within a temperature 
range of -10 to -23°C and be fitted with a temperature 
alarm device to give a warning when the refrigerator 
temperature approaches the upper safety limit. It may 
be desirable for one deep-freeze refrigerator at each 
hospital to be supplied from the essential circuits where 
this can be conveniently arranged. 

E-3. 2 In milk kitchen, all refrigerators should be 
supplied from an essential circuit. 

E-3.3 Where electrically operated pumps are used to 
maintain essential water supplies (including that for 
fire fighting purposes) it will be necessary to make 
suitable arrangements for the pumps to be connected 
to the safety supply system. 

E-3.4 Telephone exchange equipment is usually 



energized from float charged batteries having sufficient 
capacity for at least 24 h normal working. 

E-3.5 Where lifts are provided for the movement of 
patients it is desirable that one lift in each separate 
section of the hospital should be so arranged that it is 
normally connected to the essential circuits of the 
installation having automatic changeover facilities. 
These lifts will be regarded as emergency or fire lifts, 
and should be suitably indicated by markings at each 
landing. 

Suitable manually-operated switching arrangements 
should be provided to enable the general safety supply 
system to be switched from the emergency lift to each 
of the other lifts in turn to eliminate the possibility of 
occupants being trapped in the lifts during power 
failures. Under normal supply conditions the 
emergency lifts only will be connected to the essential 
circuit of the installation. 

E-3.6 Communication equipment should be connected 
to essential circuits. 

E-3.7 All boiler house supplies should be fed from 
essential circuits. 

E-3.8 Emergency supplies for computers should be 
examined in each case. 



248 



NATIONAL ELECTRICAL CODE 



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Mains transformer 

Special safety supply system (motor-generator or inverter with batteries switch-over time < 15 s) 

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SP 30 : 2011 



SECTION 5 HOTELS 



FOREWORD 

Hotels lodging or rooming houses are of a wide variety, 
ranging from simple dormitory type accommodation 
for guests, where only a common bath is provided with 
no facility for dining/kitchen to the sophisticated star 
hotels. Increasing competition in the hotel industry as 
such, coupled with the demand by guests for a variety 
of comforts, calls for an electrical installation in a hotel 
with increased sophistication. 

The electrical needs of a hotel depend on the type and 
extent of facilities being provided and the rating of the 
hotel. The system design would in general be identical 
with that of any other large building, the actual power 
requirement expressed in terms of per-unit area or per 
guest room. 

Specific requirements for installations in swimming 
pool are covered in Annex A to this Section. These 
requirements also apply to swimming pools in other 
occupancies, say sports buildings. For editorial 
convenience, these specific requirements form part of 
this section of the Code. 

1 SCOPE 

This Section 5 of the Code covers requirements for 
electrical installations in buildings such as hotels and 
lodging houses. 

2 REFERENCES 

This Part 3/Section 5 of the Code should be read in 
conjunction with the following Indian Standards: 

IS No, Title 



3646 (Part 2): 1966 



8061 : 1976 



IS AEC 60309-1: 

2002 

IS/EEC 60309-2 
2002 



SP 7 : 2005 
SP 72 : 2010 



Code of practice for interior 
illumination: Part 2 Schedule for 
values of illumination and glare 
index 

Code of practice for design, 
installation and maintenance of 
service lines upto and including 
650 V 

Plugs, socket-outlets and couplers 
for industrial purposes: Part 1 
General requirements (first revision) 
Plugs, socket-outlets and couplers 
for industrial purposes: Part 2 
Dimensional interchangeability 
requirements for pin and contact 
tube accessories (first revision) 
National Building Code of India 
National Lighting Code 



3 TERMINOLOGY 

For the purpose of this Section, the definitions given 
in Part 1 /Section 2 of the Code shall apply. 

4 CLASSIFICATION 

4.1 The electrical installations covered in this Section 
are those in buildings intended for the following 
purposes: 

a) Lodging or rooming houses — These include 
any building or group of buildings in which 
separate sleeping accommodation for a total 
of not more than 15 persons on either transient 
or permanent basis with or without dining 
facilities, but without cooking facilities for 
individuals, is provided. 

NOTE — The above is distinct from single or two family 
private dwellings which are covered in Part 3/Sec 1 of 
this Code. 

b) Hotels — These include any building or group 
of buildings in which sleeping 
accommodation is provided with or without 
dining facilities for hire to more than 15 
persons, who are primarily transient such as 
hotels, inns, clubs and motels. 

NOTE — For the purpose of this Code, restaurants other 
than those forming part of a large hotel are treated as 
assembly buildings and are covered in Part 3/Sec 3 of 
this Code. 

4.2 The electrical installations in hotels covered in this 
Section include the following services: 

a) Supply intake, 

b) Main distribution centre, 

c) Ventilation and exhaust systems, 

d) Kitchen, 

e) Laundry, 

f) Cold storage, 

g) Health club, 

h) Swimming pool and filtration plants, 

j) Restaurants and bars, 

k) Interior lighting, 

m) Telephones, 

n) Channelized music, 

p) Service lifts and passenger lifts, 

q) Offices, 

r) Fire protection and alarm systems, 

s) Banquet halls and conference facilities, 

t) Gardens and parking lots and illumination 
systems therein, 



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u) Illuminated signs, display lights and 

decorative illuminations, and 
v) Emergency system. 

5 GENERAL CHARACTERISTICS OF 
INSTALLATIONS 

General guidelines on the assessment of characteristics 
of installations in buildings are given in Part 1/Sec 8 of 
this Code. For the purposes of installations falling under 
the scope of this Section, the characteristics defined 
below generally apply (see also SP 7). 

5*1 Environment 

5.1.1 The following environmental factors apply to 
hotels: 

Environment Characteristics Remarks 

(1) (2) (3) 



Utilization 

(i) 



Characteristics 

(2) 



Remarks 

(3) 



Presence of 
water 



Probability of 
presence of water 
is negligible 



Presence of 
foreign solid 
bodies 



Presence of 
corrosive or 
polluting 
substances 



Possibility of jets 
of water from any 
direction 

Possibility of 

permanent and 

total covering by 

water 

The quantity or 

nature of dust or 

foreign solid 

bodies is not 

significant 

The quantity and 

nature of corrosive 

or polluting 

substances is not 

significant 



Majority of 
locations in hotels. 
Traces of water 
appearing for short 
periods are dried 
rapidly by good 
ventilation. 
Applies to gardens 



Locations such as 
swimming pools 



For hotels situated 
by the sea or 
industrial zones, 
other 

categorization 
applies (see 
Part 1/Section 8 of 
this Code) 



Mechanical Impact and 
stresses vibration of low 

severity 
Seismic 
effect and 
lighting 



Depends on the 
location of the 
building 



5.2 Utilization 

5.2.1 The following aspects of utilization shall apply: 



Capability of Ordinary, 
persons uninstructed 

persons 



Persons 
adequately 
advised or 
supervised by 
skilled persons 

Persons in non- 
conducting 
situations 



A major 
proportion of 
occupants in 
Hotels 

Applies to areas, 
such as building 
substation and for 
operating and 
maintenance staff 



Contact of 
persons with 
earth 
potential 

Condition of 
evacuation 
during 
emergency 



Low density 
occupation, easy 
conditions of 
evacuation 

High density 
occupation, 
difficult 
conditions of 
evacuation 

Nature of No significant 
processed of risks 
stored 
material 

Contamination 
risks due to 
presence of 
unprotected food 
stuffs 



Applies to lodging 
houses 



Large hotels, high- 
rise buildings. 



Applies to 
kitchens 



6 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

6.0 Exchange of Information 

6.0.1 Proper coordination shall be ensured between the 
architect, building contractor and the electrical engineer 
on the various aspects of installation design. In addition 
to the general aspects which require coordination and 
identified in other sections, information shall be 
obtained on the following services: 

a) Whether central air-conditioning system is 
intended. If so, layout of air handling units, 
fan coil units, ducting, false ceiling and chilled 
water lines should be obtained. 

b) Whether centrally controlled fire-fighting is 
intended. If so, layout of fire-fighting 
installation should be obtained. 

c) Whether telephone and TV facilities are 
intended in each room. If so, layout of the 



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telephone installation and TV circuits should 
be obtained, 
d) Whether centrally heated out water system is 
intended. If so, layout of hot water pipe-line 
be obtained. 

6.1 Branch Circuits 

6.1.1 The general provisions for the design of wiring 
of branch circuits shall conform to those laid down in 
Part 1/Section 9 of this Code. However, for special 
cases such as for communication networks, fire-alarm 
system, etc, as well as in areas such as kitchen, laundry, 
etc, the recommendation of the manufacturer shall 
apply. 

6.1.2 The branch circuit calculations shall be done as 
laid down in Part 1/Section 1 of this Code. The specific 
demands of the lighting, appliance and motor loads, 
as well as special loads encountered in hotel building 
shall be taken into account. 

6.1.3 In hotel buildings, the interior decor normally 
includes false ceiling, carpets and curtains. Any wiring 
laid above the false ceiling should be adequately 
protected, such as by drawing the wires in metallic 
conduits and not run in open. Wires shall not be laid 
under carpets. They shall be run at skirting level and 
encased for mechanical protection. 

6.1.4 Panel Boards and Switch-boards 

The provisions of Part 1/Section 9 of this Code shall 
apply. 

6.1.5 Socket-outlets and Plugs 

6.1.5.0 These should be provided in all places where 
plug-in service is likely to be required, to reduce the 
need for alterations and extensions of wiring after the 
hotel building is completed. Duplex or other suitable 
outlets should be provided as required in the offices 
and work places for fans, lamps and appliances. The 
socket-outlets shall preferably have covers. Corridors 
and staircases shall be provided with sufficient socket- 
outlets for floor cleaning appliances. These shall be 
connected in a circuit separate from the circuits for 
the guest rooms. 

6.1.5.1 If provided, use of a central radio receiving 
system wired with multi-channels piped music system 
to each room is recommended so that the occupant may 
choose one of the broadcasts. For such reception, 
special aerials and related wiring are required. Aerial 
outlets at rooms are required for portable radios in areas 
and buildings where reception is poor but in general 
the aerial built in the set may be adequate. 

6.1.5.2 Special convenience outlets in corridors at 
suitable locations are desirable for use of portable 



equipment such as floor cleaning appliances. They 
should be of the 3 -pin type, suitably rated with one- 
pin earthed. 

Heavy duty sockets should also be provided in pantries, 
kitchens, toilets and utility rooms for use of appliances. 

Adequate plug-in sockets at proper locations should 
be provided in banquet halls and other meeting places 
for flood lights and other appliances. 

6.2 Feeders 

The general provisions laid down in Part 3/Section 9 
of this Code shall apply. 

6.3 Service Lines 

The general provisions laid down in IS 8061 shall 
apply. 

6.4 Building Substation 

6.4.1 If the load demand is high which requires supply 
at voltage above 650 V a separate indoor 
accommodation, as near the main load centre of the 
hotel as possible shall be provided to accommodate 
switchgear equipment of supply undertaking and 
indoor/outdoor accommodation for the transformers. 
The main distribution equipment of the hotel shall 
preferably be located next to the substation. Separate 
feeders shall be provided for major loads like central 
air-conditioning, kitchen, laundry, swimming pool, 
lighting of main building and other essential loads. 

6.4.2 The supply line should preferably be brought into 
the building underground to reduce the possibility of 
interruption of power supply. The accommodation for 
substation equipment as well as for main distribution 
panel shall be properly enclosed so as to prevent access 
to any unauthorized person. It shall be provided with 
proper ventilation and lighting arrangement. 

6.4.3 The location and layout of building sub-station 
and emergency diesel generating set(s) shall be in 
conformance with Part 2 of this Code. 

6.5 System Protection 

6.5.1 General 

The general rules for protection for safety laid down 
in Part 1/Section 7 of this Code shall apply. Reference 
should be made to SP 7 for guidelines for fire protection 
of buildings. 

6.5.2 For lodging and rooming houses of 3 storey and 
above, with a floor area more than 200 m 2 with central 
corridor and rooms on either side, besides fire fighting 
equipment, manually operated electric fire-alarm system 
shall be provided. Both manually operated and automatic 
fire-alarm systems shall be provided in large hotels. 



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6.6 Building Services 

6.6.1 Lighting 

6.6. LI The general rule laid down in Part 1 /Section 14 
of this Code shall apply. The choice of lighting fittings 
and general lighting design together with power 
requirements shall be planned based on the 
recommended values of illumination and limiting 
values of glare index given in Table 1 [see also IS 3646 
(Part 2) and SP 72]. 

Table 1 Recommended Values of Illumination 
and Glare Index for Hotels 

SI Building Illumination, Limiting Glare 

No. lux Index 

(1) (2) (3) (4) 



i) Entrance halls, lobby 




150 


— 


ii) Reception and accounts 




300 


— 


iii) Dining rooms (tables) 




100 


— 


iv) Lounges 




150 


— 


v) Bedrooms: 








a) General 




100 


— 


b) Dressing tables, bed 


200 


— 


heads, etc. 








vi) Writing tables 




300 


__ 


vii) Corridors 




70 


— 


viii) Stairs 




100 


— 


ix) Laundries 




200 


25 


x) Kitchens 




200 


25 


xi) Goods/passenger lifts 




70 


__ 


xii) Cloakrooms/toilets 




100 


— 


xiii) Bathrooms 




100 


— 


xiv) Shops/stores 




150-300 


22 


NOTE — The lighting 


of 


some of these 


locations is 


determined primarily by 


aesthetic considerations and the 


above values should be taken as a guide only. 





6.6.1.2 In guest bedrooms, it shall be possible to switch 
the general lighting not only from the entrance but also 
from the bedside (see also 8.4.2) 

6.6.1.3 In bathrooms, the lights should be mounted at 
head level on both sides of the mirror. Care shall be 
taken to ensure that there is no glare. 

6.6.1.4 Lighting in banquet halls shall be given special 
consideration in view of its multipurpose utility such 
as fairs, dances, fashion shows, conferences, exhibition 
or concerts. Sufficient number of controlled socket- 
outlet circuits shall be combined in a switching station 
from which the entire hall shall be visible. 

6.6.1.5 In designing outdoor lighting installations, care 
shall be taken to ensure that disturbing glare does not 
reach the rooms of the guests. 

6.6.2 Air-conditioning 

The provisions of Part 1 /Section 14 of this Code shall 
apply. 



6.6.3 Lifts and Escalators 

6.6.3.0 The general rules laid down in Part 1 /Section 14 
of this Code shall apply. However, the design of lifts 
shall take into account the following recommendations. 

6.6.3.1 Occupant load 

For hotel buildings, an occupant load of 12.5 gross 
area, in m 2 per person is recommended. 

6.6.3.2 Passenger handling capacity 

The passenger handling capacity expressed in percent 
of the estimated population that has to be handled in 
the 5 min peak period shall be 5 percent for hotel 
buildings. 

6.6.3.3 Car speed — This shall be as follows: 

Occupancy Floors Served Car Speed 

m/s 

(1) (2) (3) 



Passenger lifts for low 
and medium class 
lodging houses 
Hotels 



4-5 



0.5 



0.5-0.75 



6.6,3.4 For hotel buildings, it is desirable to have at 
least a battery of two lifts at convenient points of a 
building. If this is not possible, it is advisable to have 
at least two lifts side by side at the main entrance, and 
one lift at different sections of the building for 
intercommunication. 

7 TESTING OF INSTALLATION 

The various tests on the installation shall be carried 
out as laid down in Part 1/Section 10 of this Code. 

8 MISCELLANEOUS PROVISIONS 

8.1 Call System 

The general provisions for electrical bells and call 
system shall conform to those laid down in Part 1/ 
Section 14 of this Code. The call system should be a 
wired electrical system whereby customer may signal 
for attendance from his room. Two types of systems 
are recommended: 

a) A simple one-watt signal system which 
connects the room side call stations with a 
signal at the attendant station. It 
simultaneously lights a dome light over the 
door of the room from which the call is 
originated. The signal at the attendant station 
may be in the form of an annunciator with a 
buzzer or a light with a buzzer. 

b) A central control panel shall, be set up 



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preferably on the ground floor incorporating 
a set of indicating panels according to the 
number of wings. Each indicating panel 
should have a set of small lamps according to 
the number of rooms. After- attending the 
customer, the attendant presses the resetting 
button which puts the whole equipment to the 
original condition. 

8.2 Telephones 

A centralized EPABX System with sufficient P&T lines 
shall be installed for internal and external 
communications with the help of operator's assistance 
as well as directly through this system. These may be 
connected on a dial system which permits internal 
communication through the hotel switchboard without 
the assistance of the operator. At all the rooms, 
telephone jacks shall be installed so that a telephone 
may be plugged in any time at any convenient location. 
Parallel telephones may be provided in the bedrooms. 
Each room shall also be provided with jacks for Broad 
Band Multi Service facility /internet facility. 

8.3 Clock Systems 

The general provisions for clock systems shall conform 
to those laid down in Part 1/Sec 14. The following 
locations may be provided with clocks: 

a) Guest rooms, 

b) Main lobby, 

c) Telephone switchboard, 

d) Dining room, 

e) Banquet halls, 

f) Kitchen, and 

g) Restaurant and bar rooms. 



8.4 Emergency Supply 

See also Part 2 of this Code. 

8.4.1 In the event of a failure of supply, a large standby 
power supply usually a diesel driven generating set 
could be used to partly or entirely supply the loads in 
the hotel. Emergency lighting shall be confined to 
essential areas, and the standby power supply shall feed 
essential and safety installations in the hotel. 

8.4.2 Part of the kitchen, storage and refrigeration 
rooms in the hotel shall also be supplied by the 
emergency supply. A part of the lighting in each room, 
corridor, staircases and other circulation areas shall be 
connected to emergency supply. 

8.5 Other Special Installations 

The list of such installations is given below: 

a) TV sets at main assembly areas and in guest 
rooms, 

b) Lighting in banquet halls, 

c) Fire-fighting system, 

d) Swimming pool (see Annex A), 

e) Cold storage, 

f) Sauna Heaters (see Annex B), and 

g) Broad Band Multi Service facility /internet 
facility. 

H.6 For particular requirements for locations containing 
a bathtub or shower basin, see Annex A of Part 3/ 
Section 1 of this Code. 

8.7 Luminous Sign 

Photo luminescent safety signage should be provided 
at different strategic locations. 



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ANNEX A 
(Clause 8.5) 

PARTICULAR REQUIREMENTS FOR SWIMMING POOL 



A-l SCOPE 

This Annex applies to the basins of swimming pools 
and paddling pools and their surrounding zones where 
susceptibility to electric shock is likely to be increased 
by the reduction of body resistance and contact with 
earth potential. 

A-2 CLASSIFICATION OF ZONES 

A-2.1 Reference is drawn to Fig. 1 and Fig. 2. 

Zone — is the interior of the basin. 

Zone 1 — is limited by a vertical plane 2 m from the 
rim of the basin by the floor or the surface expected to 
be occupied by persons and the horizontal plane 2.50 m 
above the floor of the surface. 

Zone 2 — is limited by the vertical plane external to 
Zone 1 and a parallel plane 1.50 m from the former, 
by the floor or surface expected to be occupied by 
persons and the horizontal plane 2.50 m above the floor 
or surface. 

NOTE — Where the pool contains diving boards, spring boards, 
starting blocks or a chute, Zone 1 comprises the zone limited 
by a vertical plane situated 1.50 m around the diving boards, 
spring boards and starting blocks, and by the horizontal plane 
2.50 m above the highest surface expected to be occupied by 
the persons. 

A-3 PROTECTION FOR SAFETY 

A-3.1 Where safety extra-low voltage is used, whatever 
the nominal voltage, protection against direct contact 
shall be provided by barriers or enclosures affording 
at least a protection of IP2X, or insulation capable or 
withstanding a test voltage of 500 V for 1 min. 

A-3.2 All extraneous conductive parts in Zones 0, 1 
and 2 shall be bonded with protective conductors of 
ail exposed conductive parts situated in these Zones. 

A-4 SELECTION OF EQUIPMENT 

A-4.1 Electrical equipment shall have at least the 
following degrees of protection: 



a) Zone 

b) Zone 1 



IPX 8 
IPX 4 



c) Zone 2 : IP X 2 for inside swimming pools. 
IP X 4 for outside swimming pools. 

A-4.2 For Zone 1 and Zone 2, water jet is likely to be 
used for clearing purpose : IP X 5 

This requirement does not apply to instantaneous water 
heaters complying with IS 302 (Part 2/Sec 35). 

A-5 WIRING SYSTEMS 

A-5.1 In Zone and Zone 1, wiring systems shall be 
limited to those necessary to the supply of appliances 
situated in those zones. 

A-5.2 Junction boxes are not permitted in Zone and 
Zone 1. In Zone 2, they are permitted provided they 
have the necessary degree of protection as given 
in A-4.1. 

A-5.3 In Zone and Zone 1 no switchgear and 
accessory shall be installed. In Zone 2 socket-outlets 
are permitted only if they are either: 

a) supplied individually by an isolating 
transformer, or 

b) supplied by safety extra low voltage, or 

c) protected by a residual current protective 
device. 

A-5.4 If it is not possible to locate socket-outlets 
may be installed only if they are complying 

a) Outside 1.25 m from the Zone border, and 

b) protected by residual current protection device. 

A-5.S The socket-outlets shall comply IS/IEC 60309 
(Part 1) and IS/IEC 60309 (Part 2). 

A -5.6 An electric heating unit embedded in the floor 
in Zones 1 and 2 shall incorporate a metallic sheath 
connected to the local supplementary equipotential 
bonding and shall be covered by the metallic grid 
required by A-3.2. 

A-5.7 In Zone 2, only water heaters are permitted 
excepting that other equipment supplied by SELV 
(Safety Extra Low Voltage) at a nominal voltage not 
exceeding 12 V may be installed. 



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T" 



ZONE 2 



20fl£ 1 






« h J" 




lit I I 



L ^-Sm ■ Hj J 



T 

I 
I 
I 

' t 

I ZONE 2 



i 



I 



Fig. 1 Zone Dimensions for Basins Above Ground 



"T 



ZONE 2 



r~--~-T-r-T 



ZONE 1 



/?/////}//////// 



1-S m ' 2*0 

-■ m ^ m 




£ — ^ 



%///////\>/////\' 



I- 2-0m 



ZONE 2 



I 

s 

I 
I 



m hSm -«| 



Fig. 2 Zone Dimensions of Swimming Pools and Paddling Pools 



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ANNEX B 
(Clause 8.5) 

PARTICULAR REQUIREMENTS FOR LOCATIONS CONTAINING SAUNA HEATERS 



1 SCOPE 

The particular requirements of this Annex apply to 
locations in which hot air sauna heating equipment is 
installed. 

B-2 CLASSIFICATION OF TEMPERATURE 
ZONES 

B-2.1 The assessment of the general characteristics of 
the location shall take due consideration of the 
classification of the four temperature zones which are 
illustrated in Fig. 3. 

B-3 PROTECTION FOR SAFETY 

B-3.1 Where Safety Extra Low Voltage (SELV) is 
used, irrespective of the nominal voltage, protection 
against direct contact shall be provided by one or more 
of the following: 



a) insulation capable of withstanding a test 
voltage of 500 V ac, rms for 1 min. 

b) barriers or enclosures, affording at least 
degree of protection IP 24. 

B-3,2 All extraneous conductive parts shall be bonded 
with protective conductors of all exposed conductive 
parts situated in these zones and earthed. 

B-4 SELECTION OF EQUIPMENT 

B-4.1 All equipment shall have at least the degree of 
protection IP 24. 

B-4.2 Equipment should be selected in accordance with 
the temperature zones as depicted in Fig. 3 as per the 
following details: 

a) Zone A: only the sauna heater complying with 
relevant safety standard and equipment 



"T" 

0.3 m 

T 



D 



0.5 m 




0.5m- 



£T 




0.5m 



Fig. 3 Classification of Temperature Zones 



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SP 30: 2011 



directly associated with it shall be installed. 

b) Zone B: there is no special requirement 
concerning heat resistance of equipment. 

c) Zone C: equipment shall be suitable for an 
ambient temperature of 125°C. 

d) Zone D: only luminaries and their associated 
wiring, and control devices for the sauna 
heater and their associated wiring shall be 
installed. The equipment shall be suitable for 
an ambient temperature of 125°C. 

B-5 WIRING SYSTEMS 

B-5.1 Flexible elastomer insulated and mechanically 



protected cords complying with appropriate standard, 
suitable for 150°C should be used. 

B-5.2 Switchgear not built into sauna heater, other than 
a thermostat and a thermal cut-out shall be installed 
outside the hot air sauna. 

B-5. 3 Except as permitted in B-4.2 and B-5.2 
accessories shall not be installed within the hot air 
sauna. 

B-6 OTHER FIXED EQUIPMENT 

B-6.1 Luminaries shall be so mounted as to prevent 
overheating. 



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SECTION 6 SPORTS BUILDINGS 



FOREWORD 

The design and erection of electrical installation in a 
sports building have to take into account a multitude 
of factors that are unique to the type of use to which it 
is put. In a way the electrical power needs and the 
external influences in a sports building are quite 
identical to those for theatres and other multipurpose 
buildings for cultural events excepting that for 
international events exacting standards of services and 
flexibility had to be provided in a multipurpose sports 
stadia. 

Several stadia, especially those of the indoor type are 
meant for staging a variety of games which between 
themselves require varying standards of lighting levels. 
The design of illumination system in a sports building 
therefore requires consultations with a specialist and 
the guidelines provided in this Section are purely 
recommendatory in nature in this respect. 

In indoor stadia where large number of people 
congregate it is essential to inbuild adequate fire 
precautions from the point of view of safety. Assessing 
the need for adequate strength of a standby supply for 
essential services requires special consideration. 

It is to be noted that a sports stadia should preferably 
be designed for use for other purposes as well, such as 
the staging of cultural events and this aspect shall be 
borne in mind while designing the electrical needs of 
the complex so as to ensure optimum utilization of the 
facilities. 

With the advent of sophisticated stadia in the country 
as well as keeping in view the accent on sports, this 
Section of this Code has been set aside to cover such 
of those specific requirements applicable to sports 
buildings from the electrical engineering point of view. 
Taking note of the fact that the type of buildings and 
their needs for the purposes of sports and games would 
be quite different between them, only broad guidelines 
are outlined in this Section. It is recommended that 
assistance of experts shall be sought in the design of 
the installation at the early stages itself. 

1 SCOPE 

This Part 3/Section 6 of the Code covers requirements 
for electrical installations in sports buildings and stadia, 
indoor and outdoor. 

2 TERMINOLOGY 

For the purpose of this Section, the definitions given 
in Part 1/Section 2 of this Code shall apply. 



3 CLASSIFICATION OF SPORTS BUILDINGS 

3.1 The buildings for the purposes of conducting sports 
and games are characterized by the criteria that large 
number of people congregate. Sports complexes not 
basically meant for exhibition purposes, and not likely 
to be utilized for other purposes, such as for staging 
special or cultural events, shall however conform to 
the special requirements of this Section. The type of 
building shall therefore be classified as follows: 

a) Based on type of building: 

1) Indoor stadia. 

2) Outdoor stadia: Stadia meant for use in 
daylight. Stadia meant for use during 
night under artificial lighting. 

b) Based on type of game/sport: 

1) Single game sports hall/stadia. 

2) Multigames hall/stadia. 

c) Based on utility: 

1) Stadia meant for games only. 

2) Multipurpose stadia for other amuse- 
ments as well. 

d) Based on audience-factor: 

1) Stadia/halls meant for exhibition pur- 
poses — where groups of people con- 
gregate. 

2) Stadia/halls meant for training and pass- 
time — where audience may not normal- 
ly be present. 

NOTE — Classification d (1) includes stadia meant for 
staging tournaments and events, and d (2) includes 
games halls in educational institutions and the like 
where normally no exhibition is intended. 

3.1.1 Reference should be made to 5.5.1.2 for 
classification from lighting consideration. 

3.2 The electrical installation needs in sports buildings 
would therefore be governed by the type of use 
indicated in 3.1(a) to (d). A large sports complex may 
include the following sub-units: 

a) Supply intake/voltage of supply; 

b) Main substation and satellite substations, if 
any; 

c) Central control room/switch rooms; 

d) Electrification of restaurant, health clubs; 
hospitals, offices and other support structures; 

e) Communication facilities (telephone, telex, 
telegraph, data processing TV, radio and press 
facilities); 



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f) Fire protection services; 

g) External electrification of gardens and 
parking lots, service routes, lake fountains (if 
any); 

h) Emergency electric supply system including 
uninterrupted power requirements; 

j) Audio systems, public address/security; 

k) De-watering arrangements, sewage disposal, 
water supply systems; 

m) Gas/oil arrangements for sports flame if 
required; and 

n) Miscellaneous requirements for power- 
socket, microphone outlets, score-boards, etc. 

4 GENERAL CHARACTERISTICS OF SPORTS 
BUILDINGS 

General guidelines on the assessment of characteristics 
of installations in buildings are given in Part 1/Section 8 
of this Code. For the purposes of installations falling 
under the scope of this Section, the characteristics given 
below shall apply. 

4.1 Environment 

4.1.1 The following environmental factors apply to 
sports buildings: 

Environment Characteristics Remarks 

(1) (2) (3) 



Presence of 
water 



Presence of 
foreign solid 
bodies 



Submersion, Locations such as 

possibility of swimming pools 

permanent and total where electrical 
covering by water equipment is 

permanently and 
totally covered 
with water under 
pressure greater 
than J bar. 

The quantity or Indoor stadia, 
nature of dust or 
foreign solid bodies 
is not significant 

Presence of dust in Outdoor stadia, 
significant quantify 



Presence of 
corrosive or 
polluting 
substances 



Negligible 



Lighting Negligible 



260 



Covers majority 
of cases. Stadia 
and games 
complexes 
situated by the sea 
or industrial zones 
require special 
consideration. 

Covers category 
d(2) (see 3.1) type 
of installations. 



Environment Characteristics Remarks 
(1) (2) (3) 

Indirect exposure Installations 

to lighting, where supplied by 

hazard from overhead lines. 

supply 

arrangements 

exists 

Direct exposure or Lighting towers 
hazard from in outdoor stadia, 

exposure of 
equipment is 
present 

4.2 Utilization 

The following aspects utilization shall apply: 



Utilization 

(i) 



Characteristics 
(2) 



Remarks 
(3) 



Capability of 


Uninstructed 


In sports stadia the 


persons 


persons 


sportsmen and 
spectators fall under 
this category. However, 
electrical operating 
areas are accessible to 
instructed persons only. 


Conditions of Low density 


Training halls and the 


evacuation in 


occupation, easy 


like where people do 


an emergency 


conditions of 
evacuation 


not congregate. 




High density 


Large multipurpose 




occupation, 


stadia for exhibition 




difficult conditions 


purposes. 




of evacuation 




Nature of 


Existence of fire- 


Due to furniture and 


processed of 


risks. 


false floor for playing 


stored 




area 


material 







5 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

5.0 Exchange of Information 

5.0.1 Proper coordination shall be ensured between the 
architect building contractor and the electrical engineer 
on the various aspects of the installation design. In 
addition to the general aspects which require 
coordination and identified in other sections, the 
following data shall specifically be obtained: 

a) The total electrical power needs of the stadium 
including the standby power arrangements, 
which will decide the voltage of supply, 
number of substations and their preferred 
locations, capacity of diesel engine generating 

NATIONAL ELECTRICAL CODE 



SP 30: 2011 



sets for standby supply, transformers, 
switchgear, voltage stabilizers, uninterrupted 
power supply requirements, etc; 

b) In case of indoor stadia, whether air- 
conditioning is required and if so, the capacity 
and locations of main plants, air-handling 
units, pumps, ducting, layout, route of chilled 
water lines, etc. In case of outdoor stadium, 
the covered portions like offices, restaurants, 
are to be air-conditioned or not and their 
details as above; 

c) Details of fire fighting system/fire alarm 
system envisaged; 

d) Details of water supply arrangements, storm 
water drainage, sewage disposals and pump 
capacities, locations, etc; 

e) Locations of substations, switchrooms, 
distribution boards, etc; 

f) Requirements of audio-communication 
system for the stadium which includes public 
address system, car calling system, ambulance 
call, fire service call, intercom stations, 
wireless paging system, inter-stadia commu- 
nication facilities, computer-aided results 
information, etc; 

g) Details of score-boards — that is whether and 
their power etc, centralized manual or 
automatic, etc, needs, voltage stability, clock 
system, etc; 

h) Special requirements of press, TV, Radio, 
telecommunication, games federations, etc; 

j) Requirements of lighting, the location of 
lighting luminaries, type of light source, level 
of illumination required for various stages like 
training, TV (black and white or colour) 
coverage, etc; 

k) Requirements for power outlets, speaker 
outlets, microphone outlets, etc., in playing 
arena and field; and 

m) Other miscellaneous items like electrification 
of ancillary buildings in the sports complex, 
restaurants, gas/oil requirements for flame 
and their controls, fountain lighting system, 
car park, path way and external electrifi- 
cation. 

5.0.2 The following drawings are recommended to be 
prepared before commencing the installations work: 

a) Single line diagram for electrical distribution; 

b) Complete layout drawings indicating type and 
mounting of luminaries and conduit/cable 
installations for various services. This shall 



be prepared in coordination with civil and 
structural engineers; 

c) Wiring diagrams showing switching sequence 
of luminaries, firealarm system, public 
announcement systems, etc; 

d) In case of air-conditioning, layout of plants, 
chilled water piping routes, ducts/grill layout, 
etc; 

e) Layout of public address system envisaged; 
and 

f) Site plan indicating the location of pump 
houses for storm water drains, water supply, 
sewage and fire fighting systems, with the 
proposed source and route of power supply. 

5.1 Branch Circuits 

5.1.1 The general rules as laid down for other large 
assembly buildings (see Part 3/Section 3) and as laid 
down in Part 1 of this Code shall apply. 

5.1.2 Wiring installations for general purpose lighting 
and ventilation needs of the sports buildings shall 
conform to the requirements laid down in Part 1/Sec 1 
of this Code. It is preferable to avoid temporary wiring 
in electrical central control room. 

Whenever floodlight luminaries of more than 1 000 
W are installed, it is preferable to have individual 
branch, circuits to each of the luminaries after 
considering the economic aspects. 

Junction boxes shall be installed near the luminaries 
from which connection to the light source may be taken 
by flexible conduits. This will help maintenance work 
to be carried out without disturbing the positioning of 
the lighting fittings. 

5.1.3 Panel Boards and Switchboards 

The provision of Part 1 /Section 9 of this Code shall 
apply. In large stadia, the areas covered by the 
services shall be segregated into zones and the sub- 
distribution and distribution boards shall be so 
arranged and marked keeping in view their 
accessibility in times of need. 

5.1.4 Socket-outlets and Plugs 

For small stadia/halls, the provisions of Part 3/Section 3 
of this Code shall apply. The need for special 
convenience outlets shall be considered for services 
enumerated in 3.2(e). Utility socket outlets shall be 
provided at a height of about 0.3 m from the floor 
except in field/arena. These shall be of weather-proof 
type. 

5.2 Feeders 

5.2.1 The utility shall be consulted as to the type of 



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SP 30 : 2011 



service available, whether primary or secondary, 
single-phase or three-phase star or delta. 

5.2.2 Outdoor floodlighting installations can be made 
with either overhead or underground distribution 
feeders. From the point of view of appearance and 
minimum interference, the underground system is more 
desirable where large playing areas are involved. 

5.2.3 The underground system shall either be cables 
directly buried or cables in conduits. 

5.3 Building Substation 

5.3.1 The electrical needs of sports stadia may vary 
from 30 kVA to 1 000 kVA, according to the size of 
the installation. Usually HV supply is used for large 
multipurpose stadia where power demand is in excess 
of 500 kVA. The design of location of substation and 
the diesel generating set, if provided, shall conform to 
the requirements specified in Part 2 of this Code. 

5.3.2 The main substation for a sports building shall 
preferably be located in such a place that does not 
interfere with the movement of people congregating. 
All electrical operating areas, and control rooms shall 
preferably be segregated from public routes for the 
sporting events. 

5.3.3 Some installations may justify a separate 
transformer on each pole of the floodlighting tower 
with primary wiring to each tower. In smaller 
installations, it may be more economical to reduce 
the number of transformers by serving several 
locations from a single transformer through secondary 
wiring. 

5.3.4 For buildings staging national and international 
sports events, it shall be provided with duplicate power 
supply so that in the event of failure of one power 
supply, other one can be able to cater the total load 
intended to serve. The changeover should be 
automatic. 

5.3.5 Emergency power supply by DG set/s shall be 
provided at strategic locations to keep the general 
lighting and ventilation of the sport buildings in case 
of normal ac power failure. The changeover should be 
automatic. 

5.4 System Protection 

5.4.0 The general rules for the protection of safety laid 
down in Part 1 /Section 7 of this Code shall apply. 

5.4.1 Sports buildings are classified as 'assembly 
buildings' (Group D) from fire-safety point of view. 
Besides fire fighting equipment fire-detection and 
extinguishing system shall be provided as 
recommended below (see also SP 7): 



Description 


Fire Detection System 


(1) 


(2) 


Big halls for over 5 000 


Automatic sprinkler and 


persons 


alarm system 


Small halls, health clubs, 


Automatic sprinkler 


arena, gymnasiums, etc, 


Automatic fire alarm 


indoor with or without 


system 


fixed seats corridors for 




about 1 000 persons 




Same as above, 


Same as above 


occupancy for less than 




1 000 persons 




Small indoor games halls Automatic fire alarm 


for less than 300 persons 


system 


Grandstands, stadia for 


Manually operated fire 


outdoor gathering 


alarm systems, in offices 




and automatic fire alarm 




system in stadia, machine 




room, control room, etc 



5.5 Building Services 
5.5.1 Lighting 

5.5.1.0 The general rules laid down in Part 1/Section 1 1 
of this Code shall apply {see also SP 72). 

5.5.1.1 Special design features 

Design of sports lighting, especially in large stadia 
require considerations of not only the objects to be 
seen, the background brightness, etc, but the observer's 
location in the grandstand as well. The following shall 
be taken into account; 

a) Observers have no fixed visual axis or field 
of view. During the shifting of sight, even the 
ceiling and luminaries are likely to come into 
the line of vision. 

b) While the game is in play, the objects of regard 
are not fixed, and mostly moving in a three- 
dimensional space. 

c) It is important for observers to be able to 
estimate accurately the object velocity and 
trajectory. 

5.5.1.2 For the purposes of artificial lighting design, it 
is recommended to divide the location of sport play 
into general areas for more than one sport and areas 
for particular sport. 

General areas include field houses, gymnasiums, 
community centre halls and other multipurpose areas. 
For the purposes of lighting design, the nature of sports 
shall be divided as follows: 

a) Aerial sports (sports which are aerial in part 
or whole) — Badminton, basketball, 
handball, squash, tennis and volleyball. 



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b) Low level (games which are close to the 
ground level) — Archery, billiards, bowling, 
fencing, hockey, swimming and boxing. 

5.5.1.3 Levels of illumination 

For some representative types of sport, the 
recommended values of illumination are as given in 
Table 1. 

Table 1 Recommended Values of Illumination 



SI 


Sport 


Illumination, lux 


No. 






(1) 


(2) 


(3) 


i) 


Archery 






Target 


540 




Shooting line 


220 




Badminton 


320 




Basketball 


540 




Billiards (on table) 


540 




Boxing and wrestling 


540 


ii) 


Football (see Notes 1 and 2) 






Class I 


1 100 




II 


540 




III 


320 




IV 


220 


iii) 


Gymnasiums 






Matches 


540 




General exercising 


320 




Hockey (field) 


220 


iv) 


Racing 






Bicycle 


320 




Horse 


220 


v)- 


Rifle (outdoor) 






Targets 


540 (vertical) 




Firing point 


110 




Range 


54 


vi) 


Swimming 






a) Indoor Exhibition 


540 




Underwater 


100 W/m 2 of surface 
area 




b) Outdoor Exhibition 


220 




Underwater 


60 percent of indoor 




Tennis (laws) Indoor 


540 




Outdoor 


320 




Table tennis 


540 




Volleyball 


220 



NOTES 

1 It is generally conceded that the distance between the 
spectators and the play is primary consideration for 
football, as well as the potential seating capacity of the 
stand. The following classification is therefore described. 
Class I — 30 000 spectators, over 30 m minimum 

distance. 
Class II — 10 000-30 000 spectators, 

minimum distance. 
Class III — 5 000-10 000 spectators, 

minimum distance. 
Class IV — 5 000 spectators, over 10 m minimum 

distance. 

2 For football, uniform illumination shall be provided at 
ground level as well as vertically for 15 m above ground. 

1} Levels recommended are for incandescent lamps. For 
discharge lamps W/m 2 would be reduced depending upon 



over 1 5-30 m 



over 10-15 m 



the efficiency of light source, 
flux. 



In order that the installed 



5.5.1.4 Selection of light sources 

For sports lighting, the following light sources are 
advantageous together with the considerations 
indicated against each: 

a) Incandescent lamps (including tungsten 
halogen) — Where necessary, over- voltage 
operation can be used to advantage especi- 
ally as in sports installations, the lighting 
systems are used for less than 500 h a year. 

b) Fluorescent lamps — Advantageous where 
mounting heights are low and short projec- 
tion distances are acceptable, for example 
tennis, bowling, trampoline and a variety of 
indoor sports. 

c) High intensity discharge lamps — These are 
characterized by long life and high human 
efficiency. However, the inherent time delay 
for full glow when first energized or when 
there is power interruption may necessitate 
use of incandescent lighting system to provide 
emergency standby illumination in spectator 
areas. 

For sports events, where colour rendition is important, 
use of fluorescent mercury lamps is recommended. 

5.5.1.5 Miscellaneous considerations for lighting 

a) While selecting and installing high intensity 
discharge or fluorescent lamps in multipur- 
pose stadia, it is necessary to connect lamps 
on alternate phases of supply to avoid flicker 
on rapidly moving objects. Where a quite 
surrounding is required in order to avoid 
ballast hum, remote mounting of ballasts shall 
be considered. 

b) Efforts shall be required to coordinate the 
lighting design for sports events with the 
illumination requirements for TV or film 
coverage. A horizontal illumination in excess 
of 300 lux is considered adequate for 
operation of black and white TV and film 
recording. Colour recording calls for more 
stringent requirements. Colour filming may 
also need lamps having correlated colour 
temperature of between 3 000 K to 7 000 K. 
For film/TV coverage, data on the following 
shall be necessary: 

1 ) Camera sensitivity, 

2) Exposure time, and 

3) Effective aperture. 

c) Group switching — Group switching of 
luminaries is recommended to have maximum 
energy saving, after considering the following 
factors as well: 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



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SP 30 : 2011 



1) Separate switching for lighting outside 
the stadia, 

2) Requirement of lighting for training 
purpose, 

3) Requirement of lighting for tournaments 
with film and TV coverage, and 

4) Separate switching for playing arenas. 

5.5.2 Air-conditioning 

5.5.2.1 The requirements for air-conditioning and 
ventilation as laid down in Part 1/Sec 14 of this Code 
shall apply. 

5.5.3 Lifts and Escalators 

The general rules laid down in Part 1 /Section 14 of 
this Code shall apply. 

6 TESTING OF INSTALLATIONS 

The various tests on the installation shall be carried 
out as laid down in Part 1 /Section 10 of this Code. 

7 MISCELLANEOUS PROVISIONS 

7.1 Electrical Audio Systems 

The general provisions for the installation of public 
address systems shall be as laid down in Part 1/ 



Section 1 1 of this Code. 

In large grandstand stadia, the effect of time delay for 
the sound from the loudspeakers to reach different 
sections of the audience would be significant. This shall 
be avoided in taking proper precautions in the design 
of electrical audio systems. 

7.2 Control Room 

The various communication needs of large stadia is 
normally met with by electronic equipment centrally 
controlled, requiring specific power supply, and other 
installation conditions. This would call for special 
wiring systems with synchronizing systems. The 
technical requirements for these systems concerning 
voltage and frequency stability are very high. These 
shall be considered before designing the electrical 
services of the same. 

7.3 Electrical/Electronic Score Board 

The power requirements for such equipment would 
depend on the type of equipment to be installed. 
Guidelines of the manufacturer shall be adhered to. 

7.4 Clock System 

Reference shall be made to the provisions in Part 1/ 
Section 1 1 of this Code. 



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SECTION 7 SPECIFIC REQUIREMENTS FOR ELECTRICAL 
INSTALLATIONS IN MULTISTORIED BUILDINGS 



FOREWORD 

The design and construction of electrical installations 
in multistoried buildings call for special attention to 
details pertaining to fire-safety of the occupancy. 
While on the one hand, the civil design aspects are 
more stringent for high-rise buildings than for 
buildings of low heights, the electrical design 
engineer, on his part had to ensure that the fire hazards 
from the use of electric power is kept to the lowest 
possible limit. 

In drafting the requirements of electrical installations 
in various occupancies it was felt that a separate 
compendium giving the specific requirements 
applicable to multistoried buildings should be brought 
out. For editorial convenience, such details have been 
stated in this Section where the major non-industrial 
occupancies have been covered. 

In applying the provisions of this Section, note shall 
also be taken of the nature of occupancy of the high- 
rise buildings and a judicious choice of alternative 
features shall be made. 

1 SCOPE 

1.1 This Part 3/ Section 7 is intended to cover specific 
requirements for electrical installations in multistoried 
buildings. 

1.2 The requirements specified here are in addition to 
those specified in respective sections of the Code, and 
are specifically applicable for buildings more than 15 m 
in height. 

2 REFERENCES 

This Part 3/Section 7 of the Code should be read in 
conjunction with the following Indian Standards: 

IS No. Title 



SP 7 : 2005 
2309 : 1989 



10028 (Part 2) 
1981 



National Building Code of India 
Code of practice for the protection 
of buildings and allied structures 
against lightning 
Code of practice for selection, 
installation and maintenance of 
transformers: Part 2 Installation 



4 SPECIAL CONSIDERATIONS 

Special considerations shall have to be given in respect 
of the following requirements for the electrical 
installations in multistoried buildings: 



a) 



b) 
c) 
d) 
e) 
f) 
g) 
h) 

J) 
k) 
m) 



Internal wiring for lighting, ventilation, call 

bell system, outlets for appliances, power and 

control wiring for special equipments like 

lifts, pumps, blowers, etc; 

Distribution of electric power; 

Generators for standby electric supply; 

Telephone wiring; 

Fire safety; 

Lightning protection; 

Common antenna system; 

Clock system; 

Building Management System (BMS); 

EPABX with P&T lines; and 

Broad Band Multi Service facility. 



3 TERMINOLOGY 

For the purposes of this Section, the definitions given 
in Part 1 /Section 2 of the Code shall apply. 



5 EXCHANGE OF INFORMATION 

5.1 The detailed requirements of the owner shall be 
assessed at the planning stage. 

5.2 It is necessary that right at the planning stages, the 
requirements of space for accommodating the 
distribution equipment for the various electrical 
services and openings required in slabs for vertical 
risers for such services are assessed and incorporated 
in drawings in due coordination with the architect and 
structural designer. Care shall be taken to provide 
adequate and where necessary, independent spaces for 
the equipment for electrical services for different 
functions. 

5.3 Multistoried buildings are usually in framed design. 
Coordination with the architect is required in evolving 
suitable layout of lights, fans and other outlets and the 
position for their switch controls to take care of 
functional utility and flexibility. 

5.4 While designing the electrical services, due 
consideration should be given for conservation of energy. 

5.5 The voltage of supply and location of energy meters 
(especially in multistoried buildings meant for 
residential purposes) shall be agreed to between the 
utility and the owner of the building. Spaces for 
accommodating the distribution and metering 
equipment of utility should be accordingly provided 
for by coordinating with the architect and licensee. 



PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 



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SP 30: 2011 



5.6 The telephone authorities shall be consulted for 
the requirements of space for accommodating the 
distribution equipment, battery, etc, for the telephone 
services. 

5.7 The local fire brigade authorities shall be consulted 
in the matter of system layout for fire detection and 
alarm systems to comply with local bye-laws. The 
locations of control panel and indication panel shall 
be decided in consultation with the owner. 

5.8 Runs of roof conductors and down conductors for 
lightning protection shall be coordinated with the 
architects of the building. The requirements as laid 
down in Part 1/Section 15 of this Code shall be 
complied with. 

6 ASSESSMENT OF CHARACTERISTICS OF 
MULTISTORIED BUILDINGS 

6.0 The general characteristics of buildings depending 
on the type of occupancy are assessed based on me 
guidelines given in relevant sections of this Code, 
together with those given in Part 1 /Section 8. 

6.1 For the purposes of multistoried buildings in 
addition to other external influences depending on the 
type of occupancy, the electrical installation engineer 
shall specifically take note of characteristics BD2, BD4 
and CB2 given in Table 1 of Part 1 /Section 8 of this 
Code. 

7 DISTRIBUTION OF ELECTRIC POWER 

7.0 Load Assessment and Equipment Selection 

7.0.1 The electrical load shall be assessed considering 
the following: 

a) Lighting and power loads; 

b) Special loads of equipments as in laborato- 
ries, hospitals, data processing areas, etc; 

c) Air-conditioning/evaporative cooling/heating 
services; 

d) Water supply pumps; 

e) Fire fighting pumps; 

f) Electric lifts; and 

g) Outdoor and security lighting. 

The anticipated increase in load shall also be given 
due consideration. 

7.0.2 Suitable demand factors and diversity factors shall 
be applied depending on the operational and functional 
requirements. The distribution equipments shall be 
selected by adopting standard ratings. Adequate spare 
capacity should be provided for every component in 
the distribution system. 

7.0.3 The fault level at the point of commencement of 



supply should be obtained from the licencee and fault 
levels at salient points in the distribution system 
assessed. Distribution system component should be 
selected to satisfy the same. 

7.1 Building Substation 

7.1.1 The provisions contained in Part 2 of this Code 
shall apply. 

7.1.2 A substation or a switch- station with apparatus 
having, more than 2 000 litre of oil shall not ordinarily 
be located in the basement where proper oil drainage 
arrangements cannot be provided. If transformers are 
housed in the building below the ground level, they 
shall necessarily be in the first basement in a separate 
fire-resisting room of 4-h rating. The room shall 
necessarily be at the periphery of the basement. The 
entrance to the room shall be provided with a fire- 
resisting door of 2-h fire rating. A curb (sill) of a 
suitable height shall be provided at the entrance in order 
to prevent the flow of oil from a ruptured transformer 
into other parts of the basement. Direct access to the 
transformer room shall be provided, preferably from 
outside. The switchgears shall be housed in a room 
separated from the transformer bays by a fire-resisting 
wall with fire resistance of not less than 4 h. 

7.1.3 The transformer, if housed in basement, shall be 
protected by an automatic high velocity water spray 
system. The transformer may be exempted from such 
protection if their individual oil capacity is less than 
5 000 litres. 

7.1.4 In case the transformers are housed in the 
basements, totally segregated from other areas of the 
basements by 4-h fire-resisting wall/walls with an 
access directly from outside, they may be protected 
by carbon dioxide or BCF (bromochloro difluro 
methane) or BTM (bromotrifluro methane) fixed 
installation system. 

7.1.5 When housed at ground floor level, it/they shall 
be cut off from the other portion of premises by fire- 
resisting walls of 4-h fire resistance. 

7.1.6 Oil-filled transformers shall not be housed on 
any floor above the ground floor. 

7.1.7 Soak pit of approved design shall be provided 
where the aggregate oil capacity of the apparatus does 
not exceed 2 000 litres. Where the oil capacity exceeds 
2 000 litre, a tank of RCC construction of capacity 
capable of accommodating entire oil of the 
transformers shall be provided at a lower level to collect 
the oil from the catch-pit in case of emergency. The 
pipe connecting the catch-pit to the tank shall be of 
non-combustible construction and shall be provided 
with a flame-arrester [see IS 10028 (Part 2)]. 



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7.1.8 Only dry type of transformers should be used for 
installation inside the residential/commercial buildings. 

7.2 Distribution System 

7.2.0 Capacity and number of system components and 
the electrical distribution layout should be decided 
considering the likely future requirements, security, 
grade of service desired and economics. The choice 
between cables and metal rising mains for distribution 
of power should be done depending on the load and 
the number of floors to be fed. 

7.2.1 In multistoried buildings where large number of 
people gather (for example office buildings), there shall 
be at least two rising mains located in separate shafts. 
Each floor shall have a changeover switch for 
connection to either of the two mains. 

7.2.2 When cables are used for distribution to different 
floors, it may be desirable that cables feeding adjacent 
floors are interconnected for use when distribution 
cables in either of the floors fail. 

7.2.3 It is essential to provide independent feeders for 
installations such as fire lift, fire alarm, fire pumps, 
etc. 

7.2.4 In the case of residential buildings, submain 
wiring to the flats/apartments shall be independent for 
each flat/apartment. 

7.2.5 Twin earthing leads of adequate size shall be 
provided along the vertical runs of rising mains. 

7.3 Siting of Distribution Equipment 

7.3.1 The following aspects shall be considered in 
deciding the location of electric substation for 
multistoried buildings: 

a) Easy access for purpose of movement of 
equipment in and out of the substation 
including fire fighting vehicles; 

b) Ventilation; 

c) Avoidance of flooding by rain water; 

d) Feasibility of provision of cable ducts (keep- 
ing in view the bending radius of the cable), 
oil soak pits (for large transformers) and entry 
of utility 'scable(s); 

e) Transformer hum (and noise and vibration 
from diesel generating sets where provided 
as part of the substation); 

f) Where a separate building for substation is 
not possible, the same should preferably be 
at ground floor level of the multistoried 
building itself. In the case of a complex with 
a number of buildings, the substation should 
be located, as far as possible, near the load 
centre; and 



g) In the cases of certain high rise buildings, 
provision of substation at intermediate floors 
may be necessary for case of distribution. In 
such cases, non-inflammable cooling medium 
shall be used for substation equipment from 
the point of view of fire safety. 

7.3.2 The vertical distribution mains should be located 
considering the following aspects: 

a) Proximity to load centre; 

b) Avoiding excess lengths of wiring for final 
circuits and points; 

c) Avoiding crossing of expansion joint, if any, 
by horizontal runs of wiring; 

d) Avoiding proximity to water bound, areas like 
toilets, water coolers, sanitary/air- 
conditioning shafts, etc; 

e) Easy maintainability from common areas like 
lobbies, corridors, etc; and 

f) Feasibility to provide distribution switch- 
boards in individual floors vertically one over 
the other. 

7.4 Wiring Installation 

7.4.1 The electrical wiring shall be carried out in 
conformity with Part 1/Section 9 of this Code. 

7.4.2 Aluminium conductor may be used for wiring 
cables, but copper conductor may be preferred for fire- 
alarm, telephones, control circuits, etc. 

7.4.3 Where excessively long lengths of wiring runs 
are inevitable to suit the building layout, the conductor 
sizes shall be suitably designed to keep the voltage 
drop within limits {see Part 1/Section 9 of this Code). 

7.4.4 The type and capacity of control switches shall 
be selected to suit the loading, such as room air- 
conditioners, water coolers, group control of 
fluorescent lights, etc. 

7.4.5 All switchgear equipment used for main- 
distribution in multistoried buildings shall be metal 
enclosed. Woodwork shall not be used for the 
construction of switchboards. 

7.4.6 The electric distribution cables/wiring shall be 
laid in a separate duct. The duct shall be sealed at every 
alternative floor with non-combustible materials having 
the same fire resistance as that of the duct. Low and 
medium voltage wiring running in shaft and in false 
ceiling shall run in separate conduits. 

7.4.7 Water mains, telephone lines, intercom lines, gas 
pipes or any other service line shall not be laid in the 
duct for electric cables. 

7.4.8 Separate circuits for water pumps, lifts, 



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staircases and corridor lighting and blowers for 
pressurizing system shall be provided directly from 
the main switchgear panel and these circuits shall 
be laid in separate conduit pipes, so that fire in one 
circuit will not affect the others. Master switches 
controlling essential service circuits shall be clearly 
labelled. 

7.4.9 The inspection panel doors and any other opening 
in the shaft shall be provided with airtight fire doors 
having the fire resistance of not less than 1 h. 

7.4.10 Medium and low voltage wiring running in 
shafts, and within false ceiling shall run in metal 
conduit. Any 230 V wiring for lighting or other 
services, above false ceiling, shall have 660 V grade 
insulation. The false ceiling, including all fixtures used 
for its suspension, shall be of non-combustible material. 

7.4.11 An independent and well-ventilated service 
room shall be provided on the ground floor with direct 
access from outside or from the corridor for the purpose 
of termination of electric supply from the licensees, 
service and alternative supply cables. The doors 
provided for the service room shall have fire resistance 
of not less than 2 h. 

7.4.12 If the utility agree to provide meters on upper 
floors, the utility's cables shall be segregated from 
consumers' cable by providing a partition in the duct. 
Meter rooms on upper floors shall not open into 
staircase enclosures and shall be ventilated directly to 
open air outside. 

7.4.13 The staircase and corridor lighting shall be on 
separate circuits and shall be independently connected 
so as it could be operated by one switch installation on 
the ground floor easily accessible to fire fighting staff 
at any time irrespective of the position of the individual 
control of the light points, if any. It should be of MCB 
type of switch so as to avoid replacement of fuse in 
case of crisis. 

7.4.14 Staircase and corridor lighting shall also be 
connected to alternative supply as defined in 8.1 for 
buildings exceeding 24 m in height. For assembly 
institutional buildings of height less than 24 m, the 
alternative source of supply may be provided by battery 
continuously trickle charged from the electric mains. 

7.4.15 Suitable arrangements shall be made by 
installing double throw switches to ensure that the 
lighting installed in the staircase and the corridor 
does not get connected to two sources of supply 
simultaneously. Double throw switch shall be 
installed in the service room for terminating the 
standby supply. 

7.4.16 Emergency lights shall be provided in the 
staircase/corridor. 



8 PROVISION OF STAND-BY GENERATING SET 

8.1 A centralized EPABX System with P&T lines shall 
be installed for internal connection as well as for 
external communication with essential services. The 
following loads shall be fed from the stand-by 
generating set, to enable continuity of supply in the 
event of failure of mains: 

a) Lighting in common areas, namely corridors, 
staircases, lift lobbies, entrance hall, common 
toilets, etc; 

b) Fire lift; 

c) Fire fighting pump, smoke extraction and 
damper systems; 

d) Fire alarm control panel; 

e) Security lighting; 

f) Obstruction light(s); 

g) Water supply pump; and 

h) Any other functional and critical loads. 

8.2 The norms specified in Part 2 of this Code is 
applicable for locating DG sets. 

9 TELEPHONE WIRING SYSTEM 

9.1 On the basis of assessment of demand of direct 
telephones and EPABX lines, the conduit runs for 
telephone wiring should be designed in consultation 
with telephone department. Where telephone wiring 
is intended to be taken on any other method, this should 
be coordinated with the architect and the telephone 
department. 

9.2 Lighting, ventilation and flooring in battery rooms 
should be designed in accordance with the guidelines 
in Part 2 of this Code. 

9.3 Suitable provisions should be made for cable entry 
and spaces for distribution components. 

9.4 Where the layout of intercom telephones is known 
in advance, provisions for wiring for the same may 
also be made. 

10 FIRE SAFETY 

10.1 Consideration in respect of the following 
provisions is necessary from fire safety point of view: 

a) Fire detectors and alarm system; 

b) Fire fighting arrangements; 

c) Fire lift; 

d) First-aid and fire fighting appliances; 

e) Construction of lift shafts, cable and rising 
main shafts, lobbies, substation, etc, from fire 
safety considerations; and 

f) Provision for pressurization of stairwells, lift 
shafts, lobbies, etc. 



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10.2 Provisions contained in Part 1/Section 11 of this 
Code and SP 7 shall be applicable in respect of the 
above aspects. Any regulations of fire safety by local 
municipal/fire authorities shall also be complied with. 

10.3 The following specific guidelines shall be kept in 

view. 

103.1 All buildings with heights of more than 15 m 
shall be equipped with manually operated electrical 
fire alarm (MOEFA) system and automatic fire alarm 
system. However, apartment and office buildings 
between 15 m and 24 m in height may be exempted 
from the installation of automatic fire alarm system 
provided the local fire brigade is suitably equipped for 
dealing with fire above 15 m height and in the opinion 
of the Authority, such building does not constitute 
hazard to the safety of the adjacent property or the 
occupants of the building itself. 

103.1.1 Manually operated electrical fire alarm system 
shall be installed in a building with one or more call 
boxes located at each floor. The call boxes shall 
conform to the following: 

a) The location of call boxes shall be decided 
after taking into consideration the floor plan 
with a view to ensuring that one or the other 
call box shall be readily accessible to all 
occupants of the floor without having to travel 
more than 22.5 m. 

b) The call boxes shall be of the 'break-glass' type 
where the call is transmitted automatically to 
the control room without any other action on 
the part of the person operating the call box. 
The mechanism of operation of the call boxes 
shall preferably be without any moving parts. 
However, where any moving part is 
incorporated in the design of the call box, it 
shall be of an approved type, so that there shall 
be no malfunctioning of the call box. 

c) All call boxes shall be wired in a closed circuit 



to a control panel in the control room in 
accordance with good practice so located that 
the floor number/zone where the call box is 
actuated is clearly indicated on the control panel. 
The circuit shall also include one or more 
batteries with a capacity of 48 hours normal 
working at full load. The battery shall be 
arranged to be continuously trickle charged from 
the electric mains. The circuit may be connected 
to alternative source of electric supply. 

d) The call boxes shall be arranged to sound one 
or more sounders so as to ensure that all 
appropriate occupants of the desired floor(s) 
shall be warned whenever any call box is 
actuated. 

e) The call boxes shall be so installed that they 
do not obstruct the exit-ways and yet their 
location can easily be noticed from either 
direction. The base of the call box shall be at 
a height of 1 m from the floor level. 

103.1.2 The installation of call boxes in hostels and 
such other places where these are likely to be misused, 
shall as far as possible be avoided. Location of call 
boxes in dwelling units shall preferably be inside the 
building. 

NOTES 

1 Several types of fire detectors are available in the market, 
but the application of each type is limited and has to be carefully 
considered in relation to the type of risk and the structural 
features of the building where they are to be installed. For 
guidelines for selection of fire detection reference may be made 
to relevant Indian Standard. 

2 No automatic detector shall be required in any room or portion 
of building which is equipped with an approved installation of 
automatic sprinklers. 

11 LIGHTNING PROTECTION 

Provisions of lightning protection of multistoried 
buildings shall be made in conformity with Part 1/ 
Section 15 of this Code and IS 2309. 



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PART 4 



SP 30 : 2011 



PART 4 ELECTRICAL INSTALLATIONS IN 
INDUSTRIAL BUILDINGS 

FOREWORD 

Electrical networks in industrial buildings serve the purpose of distributing the required power to the consuming 
points where it is used for a multitude of purposes in the industry. The design of electrical installation in industrial 
premises is therefore more complicated than those in non-industrial buildings. 

Industrial installation has to take care of load requirements and supply limitations in a simple and economic 
manner, ensuring at the same time full protection to human life and loss of property by fire. The network layout 
should also facilitate easy maintenance and fault localization. Keeping in view the tariff structures as also the 
economic necessity of conserving power to the maximum extent, power factor compensation assumes special 
importance. 

A particular feature of electrical installations in industrial buildings is the reliability of supply to essential operations 
for which standby and emergency supply sources/networks had to be designed. The needs of such systems would 
depend on the type and nature of the industrial works. 

Locations in industrial buildings which are by their nature hazardous, require special treatment in respect of 
design of electrical installations therein. Such special rules for hazardous areas are covered in Part 7 of the Code 
and these shall be complied with in addition to the general rules specified in this Part {see also Part 7 of this 
Code). 

In clause 4 of this Part, an attempt has been made to classify industrial installations depending on the specified 
criteria therein. Such a classification, it is hoped would help identify the specific nature of each industry and the 
locations therein, assisting the design engineer in the choice of equipment and methods. 

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 273 



SP 30 : 2011 



1 SCOPE 

1.1 This Part 4 of the Code covers the guidelines for 
design and construction of electrical installations in 
industrial buildings. 

1.2 This Part 4 does not cover specific areas in industrial 
sites, such as office buildings, workers rest rooms, 
medical facilities, canteen annexe, etc, for which 
requirements stipulated in the relevant sections of Part 3 
of the Code apply. 

1.3 This Part 4 also does not cover locations in 
industrial sites that are by nature hazardous for which 
the provisions of Part 7 of the Code apply. 

2 REFERENCES 

This Part 4 should be read in conjunction with the 
Indian Standards listed at Annex A. 

3 TERMINOLOGY 

For the purpose of this Part 4, the definitions given in 
Part 1 /Section 2 of the Code and the following shall 
apply: 

3.1 Pollution — Any condition of foreign matter, solid, 
liquid or gaseous (ionized gases), that may affect 
dielectric strength or surface resistivity 

3.2 Pollution Degree (of Environmental Conditions) 
— Conventional number based on the amount of 
conductive or hygroscopic dust, ionized gas or salt and 
on the relative humidity and its frequency of 
occurrence, resulting in hygroscopic absorption or 
condensation of moisture leading to reduction in 
dielectric strength and/or surface resistivity. 

4 CLASSIFICATION OF INDUSTRIAL 

BUILDINGS 

Industrial buildings by definition include any building 
or part of building or structure, in which products or 
materials of all kinds and properties are stored, 
fabricated, assembled, manufactured or processes, for 
example, assembly plants, laboratories, dry cleaning 
plants, pumping stations, refineries, dairies, saw mills, 
chemical plants, workshops, distilleries, steel plants, etc. 

Industrial installations are of various types and in a 
single industrial site, electrical loads of varying 
requirements are to be met. For the purpose of this 
Part, industries are classified based on three criteria as 
given in 4.1 to 4.3. 

4.1 Classification Based on Fire Safety 

4.1.1 Industrial buildings are classified into Group G 
from the fire safety point of view in SP 7. Buildings 
under Group G are further subdivided as follows: 



a) Subdivision G-l — Buildings used for low hazard 
industries — Includes any building in which the 
contents are of such low combustibility and the 
industrial processes or operations conducted 
therein are of such a nature that there are no 
possibilities for any self-propagating fire to occur 
and the only consequent danger to life and 
property may arise from panic, fumes or smoke, 
or fire from some external source. 

b) Subdivision G-2 — Buildings used for 
moderate hazard industries — Includes any 
building in which the contents or industrial 
processes of operations conducted therein are 
liable to give rise to a fire which will burn 
with moderate rapidity and give off a 
considerable volume of smoke but from which 
neither toxic fumes nor explosions are to be 
feared in the event of fire. 

c) Subdivision G-3 — Buildings used for high 
hazard industries — Includes any building in 
which the contents or industrial processes or 
operations conducted therein are liable to give 
rise to a fire which will burn with extreme 
rapidity or from which poisonous fumes or 
explosions are to be feared in the event of fire. 

NOTE — SP 7 includes Group J buildings for such 
location where storage, handling, manufacture or 
processing of highly combustible or explosive materials 
or products are being carried out. Such installations 
including such high hazard locations in Group G 
classification shall comply with the special rules of 
Part 7 of. the Code. 

4.1.2 Typical list of industries for different class of fire 
hazard are given in Annex B. 

4.2 Classification Based on Power Consumption 

4.2.1 Industrial buildings are also classified depending 
on the quantum of electric power requirements for its 
services as given in Table 1 . 

4.2.2 Loads within the industrial site could be divided 
depending on their nature and size. For guidance, the 
classification given in Table 2 shall be referred to. 

4.3 Classification Based on Pollution 

For the propose of evaluating creepage distances and 
clearances, the following four degrees of pollution in 
the micro-environment are established: 

a) Pollution degree 1 — No pollution or only 
dry, non-conductive pollution occurs. The 
pollution has no influence. 

b) Pollution degree 2 — Only non-conductive 
pollution occurs except that occasionally a 
temporary conductivity caused by 
condensation is to be expected. 



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Table 1 Classification Based on Power 
Consumption 

(Clause 4.2.1) 



SI No. 

(1) 


Description l) 

(2) 


Average 

Power 

Requirement 

(3) 


Examples 

(4) 



i) Light 

industries 
ii) Average 

industries 



iii) Heavy 
industries 



Up to 50 kVA 

Above 50 kVA 
up to 2 000 
kVA 



Above 2 000 
kVA 



' and 



Hosiery, tailoring 
jewellery 
Machinery, engine 
fitting, motor cars, 
aircraft, light pressings, 
furniture, pottery, glass, 
tobacco, electrical 
manufacturing and 
textile (see Note) 

Heavy electrical 
equipment, rolling 
mills, structural steel 
works, tube making, 
foundries, locomotives, 
ship-building and 
repairing, chemical 
factories, factories for 
metal extraction from 
ores, etc. 

NOTE — Average factory installations are set apart from 
heavy industries in that the former has no conditions 
requiring specialized or exceptional treatment. 

^Terminology based on IS 732. Where different degrees of 
hazard occupancy exist in different parts of building, the 
most hazardous of those shall govern the classification for 
the purpose. 



Table 2 Load Groups in Industrial Buildings 
(Clause 4.2.2) 



SI. 


Groups 


Type to Load 


Examples 


Corrected 


No. 








Power 
Factor 


(1) 


(2) 


(3) 


(4) 


(5) 



>0.85 



i) 1 Small and large loads Repair shop, 

fairly evenly distributed automatic 

over the whole area and lathe, 

loaded constantly during workshop, 

the working day spinning 

(precision mechanical mill, 

engineering) weaving mill 

ii) 2 Loads fairly evenly 
distributed over the 
whole area, but varying 
loads and with peak load 
at different times (for 
example metal working 
industry) 

iii) 3 Loads having very high 
power requirement in 
conjunction with smaller 
loads of negligible size 
compared to the total 
load (for example, raw 
material, industry) 



c) Pollution degree 3 — Conductive pollution 
occurs or dry non-conductive pollution occurs 



Press shop 


do 


Machine 
shop 


do 


Welding 
shop 


do 


Heat 
treatment 
shop, steel 
works, 
rolling mills 


do 



which becomes conductive due to 
condensation — which is to be expected, 
d) Pollution degree 4 — Continuous 
conductivity occurs due to conductive dust, 
rain or other wet conditions. 

NOTES 

1 Clearances and creepage distances according to the different 
pollution degrees are given in Tables 13 and 15 of IS/IEC 
60947-1. Unless otherwise stated by the relevant product 
standard, equipment for industrial applications is generally for 
use in pollution degree 3 environment. However, other pollution 
degrees may be considered to apply depending upon particular 
applications or the micro-environment. 

2 The pollution degree of the micro-environment for the 
equipment may be influenced by installation in an enclosure. 
Means may be provided to reduce pollution at the insulation 
under consideration by effective use of enclosures, 
encapsulation or hermetic sealing. Such means to reduce 
pollution may not be effective when the equipment is subject 
to condensation or if, in normal operation, it generates 
pollutants itself. 

3 Pollution will become conductive in the presence of humidity. 
Pollution caused by contaminated water, soot, metal or carbon 
dust is inherently conductive. Small clearances can be bridged 
completely by solid particles, dust and water and therefore 
minimum clearances are specified where pollution may be 
present in the micro — environment. 

5 GENERAL CHARACTERISTICS OF 
INDUSTRIAL BUILDINGS 

General guidelines on the assessment of characteristics 
of installations in buildings are given in Part 1 of the 
Code. For the purposes of installations falling under 
the scope of this Part 4, the characteristics given below 
shall apply. 

5.1 Environment 

5.1.1 The following environmental factors shall apply 
to industrial installations: 

Environment Characteristics Remarks 

(1) (2) (3) 

Presence of 
water 



Presence of 
foreign solid 
bodies 



Presence of 
corrosive 



Presence of water 
negligible, or 
possibilities of free 
falling drops or 
sprays 

These conditions 
include possibilities 
of presence of 
foreign solid bodies 
of various sizes 
likely to affect 
electrical equipment 
(such as tools, 
wires, dust, etc.) 

Atmospheric where 
the presence of 



Depends on the 
location. For 
further details 
see Part 1/Sec 8 
of the Code 

Depends on the 
location. For 
further details 
see Part 1/Sec 8 
of the Code 



Industrial 
installations, 



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SP 30 : 2011 



Environment 


Characteristics 


Remarks 


Utilization 


Characteristics 


Remarks 


(1) 


(2) 


(3) 


(1) 


(2) 


(3) 


polluting 


corrosive or 


situated by the 


Contact of 


Persons are 


Locations with 


substances 


polluting substances 


sea, chemical 


persons with 


frequently in touch 


extraneous 




is significant 


works, cement 


earth 


with extraneous 


conducting 






works where the 


potential 


conductive parts or 


parts, either 






pollution arises 




stand on conducting 


numerous or 






due to abrasive, 




surfaces 


large area 






insulating or 




Persons are in 


Metallic 






conducting 




permanent contact 


surrounding 






ducts 




with metallic 


such as boilers 




Intermittent or 


Factory 




surroundings and 


and tanks 




accidental 


laboratories 




for whom the 






subjection to 


boiler rooms, 




possibility of 






corrosive or 


etc. 




interrupting contact 






polluting chemical 






is limited 






substances being 




Conditions 


Low density 


This category 




used or produced 




of 


occupation, easy 


applies to 




Continuous 


Chemical works 


evacuation 


conditions of 


buildings of 




pollution 






evacuation 


normal or low 


Mechanical 


Impact and 


Household and 






height 


stresses 


vibration of low 


similar 


Nature of 


Existence of fire- 


Wood- working 




severity 


conditions 


processed or 


risks, where there 


shop, paper 




Impact/vibration of 


Industrial 


stored 


is manufacture, 


factories, textile 




high severity 


installations 
subject to severe 
conditions 


material 


processing or 
storage of 
flammable 
materials, including 


mills, etc 


Seismic 
effect and 




Depends on the 
location of the 




presence of dust 




lighting 




buildings 




Processing or 


Oil refineries, 










storage of low- 
flash-point 


hydrocarbon 
stores 










5.2 Utilization — The following aspects utilization 




materials including 




shall apply: 








presence of 
explosive dust 














Utilization 

(i) 


Characteristics 
(2) 


Remarks 
(3) 















Capability of Instructed persons, 
persons adequately advised 

or supervised by 
skilled persons 
(operating and 
maintenance staff) 



Persons with 

technical 

knowledge and 

sufficient 

experience 

(engineers and 

technicians) 



Majority of 
persons utilizing 
the industrial 
installations are 
in this category. 
However specific 
zones or 
operations 
involving 
uninstructed 
persons shall also 
be kept in view 

Closed operating 
areas 



5.3 Compatibility 

In industrial installations, an assessment shall also be 
made of any characteristics of equipment likely to have 
harmful effects upon other equipment or other services 
{see Part 1/Section 8 of the Code). 

5.4 Maintainability 

Assessment shall also be made of the frequency and 
quality of maintenance of the installation (see 
Part 1/Section 8 of the Code). 

6 SUPPLY CHARACTERISTICS AND 
PARAMETERS 

6*0 General 

6.0.1 The arrangement of the electrical system in 
industrial plants and the selection of electrical 
equipment depends largely on the type of 



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manufacturing process, the reliability of supply and 
adequate reserve of electrical capacity are the most 
important factors to avoid interruption of supply. 

6.0.2 All electrical installation shall be suitable for the 
voltage and frequency of supply available. 

6.0.3 For large loads, the relative advantage of high 
voltage three-phase supply should be considered. 
Though the use of high voltage supply entails the 
provision of space and the capital cost of providing a 
suitable transformer substation on the consumer's 
premises, the following advantages are gained: 

a) Advantage in tariff, 

b) More effective earth fault protection for heavy 
current circuits, 

c) Elimination of interference with supplies to 
other consumers permitting the use of large 
size motors, welding plant, etc., and 

d) Better control of voltage regulation and more 
constant supply voltage. 

6.0.4 In very large industrial buildings where heavy 
electric demands occur at scattered locations, the 
economics of electrical distribution at high voltage 
from the main substation to other subsidiary 
transformer substations or to certain items of plant, 
such as large motors, furnaces, etc, should be evaluated. 
The relative economy attainable by use of medium or 
high voltage distribution and high voltage plant is a 
matter for expert judgement and individual assessment 
in the light of experience by a professionally qualified 
electrical engineer. 

6.1 Industrial Substations 

6.1.0 The general requirements for substation 
installations given in Part 2 of the Code shall apply in 
addition to those given below. 

6.1.1 If the load demand is high, which requires supply 
at voltages above 650 V, a separate substation should 
be set up. For an outdoor substation general guidelines 
as given in Part 2 of the Code shall apply. For bringing 
the supply into the factory building, a separate indoor 
accommodation, as close as possible to the main load 
centre, should be provided to house the switchgear 
equipment. 

6.1.2 The supply conductors should preferably be 
brought into the building underground to reduce the 
possibility of interruption of power supply. The 
accommodation for substation equipment as well as 
for main distribution panel shall be properly chosen 
so as to prevent access by any unauthorized person. 
It shall be provided with proper ventilation and 
lighting. 



6.1.3 In cases where the load currents are very high, 
and the transformers are located just outside the 
building, a bus-trunking arrangement may be desirable. 
These trunkings should, however, be straight, as far as 
possible, and also as short as possible on economic 
grounds. 

6.1.4 Location of Transformers and Switchgear 

Oil filled transformers are preferably located outdoors 
while the associated switchgear is located in a room of 
the building next to the transformer. In certain cases, 
however, it may be considered desirable to locate the 
transformer inside the room. 

For reasons of safety, however, it may be considered 
desirable to locate the transformer also inside the room. 
The transformer could be connected to the switchgear 
by cables for small loads, however it may often be 
found desirable to avoid cable joints and connect the 
transformer directly to the switchgear placed on either 
side of the transformer. For oil-filled transformer, 
special means should be available for remote operation 
of the main switches/circuit-breakers in an emergency 
created by explosion/fire in the transformers. 

6.1.5 In order to ensure the reliability and safety of 
industrial sub-station, it is desirable to have circuit 
breakers as the main switching elements on both sides 
of the transformers. However, a high voltage sizes, 
switches and fuses may also be used for this purpose 
upto the limit specified under Rule 50, sub-rule 1 of 
Indian Electricity Rules, 1956. 

6.1.6 For small substations up to 1 600 kVA capacity, 
it is also possible to locate the substation at the load 
centre, without a separate room. This yields 
considerable economies in cost. In such cases, the 
transformer shall be of dry type. 

6.1.7 Isolation of Switchgear 

For installations where the system voltage exceeds 
650 V, the typical circuits and the recommended 
location of isolating switches in such circuits are 
illustrated in IS 732. Reference should be made to the 
same for guidance regarding isolation depending on 
the type of supply system. 

6.2 Distribution of Power 

6.2.1 From the main receiving station, power is taken 
to the loads, either directly as in the case of small 
factories, or through further load centre substations as 
would be the case with bigger installations. 

Distribution is done on HV through circuit breaker/ 
load break switches depending on quantum of load to 
be transferred, distance to be covered, and on similar 
factors. MV/LV distribution is possible through one 
of the following: 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



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SP 30 : 2011 



a) Wall-mounted distribution boards, 

b) Floor mounted distribution boards, 

c) Local fuse distribution boards, and 

d) Overhead bus bar system with tap-off holes. 

6.2.2 In every layout, however, specific care shall be 
taken for: 

a) Human safety, 

b) Fire/explosion hazards, 

c) Accessibility for repair/checking, 

d) Easy identification, and 

e) Fault localization. 

6,23 Switchgear 

6.23.0 All switchgear equipment used in industrial 
installations shall be metal enclosed. Woodwork shall 
not be used for mounting off switchboards. 

6.23.1 MV switchgear isolation and protection of 
outgoing circuits forming main distribution system may 
be effected by means of circuit-breakers, or switchfuse 
units mounted on the main switchboards. The choice 
between alternative types of equipment may be 
influenced by the following considerations: 

a) In certain installations where supply is from 
remote transformer substations, it may be 
necessary to protect main circuits with circuit- 
breakers operated by earth leakage trips, in 
order to ensure effective earth fault protection. 

b) Where large electric motors, furnaces or other 
heavy electrical equipment is installed, the 
main circuits shall be protected by metal-clad 
circuit-breakers or contactors of air-break or 
oil-immersed type fitted with suitable 
instantaneous and time delay over current 
devices together with earth leakage and back- 
up protection where necessary. 

c) In installations other than those referred to in 
(a) and (b) or where overloading of circuits 
may be considered unlikely to occur, HRC 
type fuses will normally afford adequate 
protection for main circuits. Where means for 
isolating main circuits is required, fuse switch 
or switch fuse units shall be used or fuses with 
switches forming part of the mean switch- 
board shall be used. 

6.23.2 It may be necessary to provide for connection 
of capacitors for power- factor correction; and when 
capacitors are to be installed advice of capacitor and 
switchgear manufacturers shall be sought. 

6.233 Adequate passageways shall be allowed so that 
access to all switchboards for operation and 
maintenance is available. Sufficient additional space 
shall be provided for anticipated future extensions. 



6.23.4 Switchboards should, preferably, be located in 
separate rooms to ensure: 

a) adequate protection against weather elements 
like heat, dust, corrosion, etc; and 

b) protection against entry of factory material 
like cotton, wood dust, water during clean- 
ing, etc. 

Where necessary the control rooms should be designed 
to avoid wide fluctuations in ambient temperature, and 
against entry of excessive dust or corrosive gases. 

6.2.3.5 Certain applications may necessitate location 
of the switchboards on the factory floor itself, without 
separate rooms. In such cases, the switchboards shall 
be specifically designed and protected against hazards 
mentioned above. 

63 Main Distribution 

63.1 For power distribution from a substation or main 
switchboard to a number of separate buildings, use shall 
preferably be made of; 

a) metal-sheathed, bedded and armoured cable, 
served, installed overhead/underground, or 

b) mineral-insulated metal-sheathed cable, 
served with PVC, laid overhead/direct in the 
ground, or 

c) PVC-insulated, armoured and PVC-sheathed 
cable installed overhead/underground, or 

d) XLPE insulated, armoured and PVC-sheathed 
cable installed overhead/underground. 

63.1.1 Cables shall not be laid in the same trench or 
alongside a water main. 

63.1.2 Cable trenches shall be made with sufficient 
additional space to provide for anticipated future 
extensions. 

63.2 Cables at difference voltage levels should be 
laid with separation at least 250 mm and clearly 
identified. Cables at voltages above 1 000 V should be 
laid at the lowest level in trenches, and at the highest 
level on walls, keeping in view the requirements of 
human safety. The cable routes where buried should 
be properly identified by route markers, as a precaution 
against accidents. The marker should necessarily 
indicate the voltage level. Cables laid underground or 
at low working levels, should either be with armouring, 
or should be adequately protected against mechanical 
damage, for example, by the use of conduits. 

6.4 Sub-circuits 

6.4.0 The sub-circuit wiring shall conform in general 
to the requirements given in IS 732. 



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6.4.1 In 3-phase distribution systems, a neutral 
conductor may preferably be provided in all sub- 
main circuits even when there is no immediate 
requirement for the supply of single-phase circuits. 
Control devices are often designed for connection 
between one phase and neutral and considerable 
extra cost may be involved, if a four-wire sub-main 
has to be installed in place of a three-wire sub-main 
previously installed. 

6.4.2 In workshops and factories where alterations and 
additions are frequent, it may be economical and 
convenient to install wiring in ducts or trunking. 
Alternatively, cables may be conveniently run on 
perforated metal cable trays. In this case earth 
continuity conductor shall be bonded to each section 
of ducts or trunking to provide permanency of the 
electrical continuity of the joints of the ducts. 

6.4.3 In machine shops and factories where alterations 
in layout may repeatedly occur, consideration shall be 
given to the replacement of local distribution boards 
by overhead bus-bar or cable systems, to which 
subcircuit are connected through fused plugs in tapping 
boxes wherever required. 

6.4.4 In industrial installations, the branch distribution 
boards shall be totally segregated for single phase 
wiring. 

6.4.5 Where more than one distribution system is 
necessary, the socket outlets shall be so selected as to 
obviate inadvertent wrong connections. 

6.4.6 In industrial premises, 3-phase and neutral socket 
outlets shall be provided with earth terminal either of 
pin type or scrapping type in addition to the main pins 
required for the purpose. 

In industrial installations, socket outlets of rating 30 A 
and above shall be provided with interlocked type 
switch. These shall be of metal clad type. 

6.4.7 Where non-luminous heating appliance is to be 
used, pilot lamps shall be arranged to indicate when 
the circuit is live. 

6.4.8 Final sub-circuits for lighting shall be so arranged 
that all the lighting points for a given area are fed from 
more than one final sub-circuit. 

6.4.9 Individual sub-mains shall be installed to supply 
passenger and goods lifts from the main or sub-main 
switchgear, and the lift manufacturer shall be 
consulted as to the appropriate rating of cables to be 
employed. 

The supply to small hoists and service lifts shall not 
be taken from a distribution board controlling final sub- 
circuits for lighting, unless the maximum current, 
including the starting and accelerating current, of the 



motor is less than 20 percent of the total rating of all 
the ways of the distribution boards. Where the supply 
is taken from such a distribution board, the motor 
circuit shall be clearly labelled. 

6.5 Selection of Wiring Systems 

The selection of a wiring system to be adopted in a 
factory depends upon the factors enumerated in Part 1/ 
Section 9 of the Code. 

The wiring system available for general use are listed 
in Annex C. Selection from a group of alternative 
systems shall be made in accordance with Annex C, 
keeping in view the particular circumstances of each 
circuit having regard to, 

a) location, structural conditions, liability to 
mechanical damage and the possibility of 
corrosion; 

b) protection against corrosion, nature of the 
corrosive elements being taken into account 
in conjunction with the protective coverings 
available; 

c) occupancy of the building; and 

d) presence of dust, fluff, moisture and tem- 
perature conditions. 

6.6 Earthing in Industrial Premises 

6.6.0 In factories and workshops all metal conduits, 
trunking, cable sheaths, switchgear, distribution fuse 
boards, starters, motors and all other parts made of 
metal shall be bonded together and connected to an 
efficient earth system. The electricity regulations made 
under the Factories Act require that adequate 
precautions shall be taken to prevent non-current- 
carrying metal work of the installation from becoming 
electrically charged. 

In larger installations, having one or more substations, 
it is recommended to parallel all earth-continuity 
system. 

6.6.1 Earth Electrodes 

Any of the earth electrodes as mentioned in Part 1 of 
the Code except cable sheath, may be used in industrial 
premises. 

6.6.2 Earth-continuity Conductor 

6.6.2.1 Earth-continuity conductors and earth wires 
not contained in the cables 

The size of the earth-continuity conductors should be 
correlated with the size of the current carrying 
conductors, that is, the sizes of earth-continuity 
conductors should not be less than half of the largest 
current-carrying conductor, provided the minimum size 
of earth-continuity conductors is not less than 1.5 mm 2 



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for copper and 2.5 mm 2 for aluminium and need not be 
greater than 70 mm 2 for copper and 120 mm 2 for 
aluminium. As regards the sizes of galvanized iron and 
steel earth-continuity conductors, they may be equal to 
the size of the current carrying conductors with which 
they are used. The size of earth-continuity conductors to 
be used along with aluminium current-carrying 
conductors should be calculated on the basis of equivalent 
size of the copper current-carrying conductors. 

6.6.2.2 Earth-continuity conductors and earth wires 
contained in the cables 

For flexible cables, the size of the earth-continuity 
conductors should be equal to the size of the current- 
carrying conductors and for metal sheathed, PVC and 
tough rubber sheathed cables the sizes of the earth- 
continuity conductors shall be in accordance with 
relevant Indian Standard. 

6.6.2.3 Conduits may be used as earth-continuity 
conductors provided they are permanently and securely 
connected to the earth system. However, where by 
nature of the process, metal conduits cannot be used 
as earth-continuity conductor on account of corrosion, 
etc, the tough rubber or PVC sheathed cables may be 
used in which case they shall incorporate an earth- 
continuity conductor. 

6.6.2.4 Flexible conduits shall not be used as earth- 
continuity conductors. A separate earth wire shall be 
provided either inside or outside the flexible conduits 
which shall be connected by means of earth clips to 
the earth system at one end and to the equipment at the 
other end. 

6.6.2.5 Earth leakage protection 

Use of earth leakage protection shall be made where 
greater sensitivity than provided by overcurrent 
protection is necessary. With a good earth electrode, 
overload protective devices may be used as earth 
leakage protective device. 

In addition to the advantage of sensitivity gained by 
such methods, the circuits may be relieved of the 
thermal and mechanical socks associated with the 
clearance of heavy faults. 

Some degree of discrimination may, in certain cases, 
be introduced with advantage by providing the delay 
in the operation of an earth-leakage trip, so that earth 
faults on smaller subsidiary circuits protected by fuses 
have time to clear and prevent the opening of the circuit- 
breaker, controlling a larger part of the installation. 

6.6.3 Earthing of Portable Appliances and Tools 

6.6.3.1 Good electrical continuity between the body 
of a portable appliance and the earth-continuity 
conductor shall always be maintained. 



6.6.3.2 It shall be ascertained that the fixed wiring at 
the appliance inlet terminals has been done correctly 
and in accordance with relevant Indian Standard. 

6.6.3.3 A single pole switch shall not be connected in 
the earth conductor. 

6.6.3.4 No twisted or taped joints shall be used in earth 
wires. 

6.6.3.5 Additional security may be obtained by 
arranging the earth-continuity conductor in the flexible 
cable between the socket outlet and the portable 
appliance in the form of a loop through which a light 
circulating current provided by a small low-voltage 
transformer is passed when the appliance is in use. Any 
discontinuity in this loop will interrupt the circulating 
current and can thus be caused to operate a relay and 
disconnect the supply from the portable appliance. 

6.6.4 Earthing of Electrically Driven Machine Tools 

In all types of machine tools connected to medium 
voltage, the body of all motors and bed plate of the 
machine shall be earthed at two places by means of a 
strip or conductors of adequate cross-sectional area. 
The strip or conductor shall be securely fastened to 
the bed plate by means of bolts. 

6.6.5 Earthing of Electric Arc Welding Equipment 

6.6.5.1 All components of electric arc welding 
equipment shall be effectively bonded and connected 
to earth. The transformers and separate regulators 
forming multioperator sets and capacitors for power 
factor correction, if used, shall be included in the 
bonding. 

6.6.5.2 All terminals on the output side of a motor 
generator set shall be insulated from the car case and 
control panel, as the generator is not connected 
electrically to a motor and therefore the welding circuit 
is electrically separate from the supply circuit including 
the earth. 

6.6.5.3 In case of transformer sets, which for welding 
purpose are double wound, an 'earth and work' terminal 
shall be provided. In single phase sets this terminal 
shall be connected to one end of the secondary winding 
and in case of three-phase sets this shall be connected 
to the neutral point of the secondary winding. 

6.6.6 Earthing of Industrial Electronic Apparatus 

6.6.6.0 The earthing of these apparatus shall follow 
normal practice but attention shall be paid to the points 
discussed below. 

6.6.6.1 Any industrial electronic apparatus which 
derives its supply from two-pin plugs incorporates 
small capacitors connected between the supply and the 



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metal case of the instrument to cut down interference. 
This capacitor shall be securely earthed. 

6.6.6.2 When an oscilloscope is being used to examine 
the wave-form of a high frequency source, the 
oscilloscope shall be earthed by a conductor entirely 
separate from that used by the source of high frequency 
power. However, when an oscilloscope is being used 
on a circuit where the negative is above earth potential 
and also connected to its metallic case, the earthing of 
the oscilloscope is not possible. Precautions shall be 
taken that in such a case the oscilloscope is suitably 
protected from other apparatus. 

6.6.6.3 High frequency induction heating apparatus 
shall be earthed by means of separate earth wire by as 
direct a route as possible. 

6.6.6.4 Dielectric loss heating equipment work at 
frequencies between 10 MHz to 60 MHz according to 
its use. These should not be directly earthed. At 
30 MHz, for example, a quarter wavelength is nearly 
250 cm and an earth wire of this length or odd multiples 
of it is capable of being at earth potential at one end 
but several hundred volts at the other end. This is due 
to the presence of standing waves on the earth 
conductors which besides being dangerous can result 
in energy being radiated to the detriment of 
communication services. In such a case it is 
recommended to mount the equipment on a large sheet 
of copper or copper gauze, the earth conductor being 
connected to it at several points. 

6.6.6.5 In case where direct earthing may prove harmful 
rather than provide safety, for example, high frequency 
and mains frequency coreless induction furnaces, 
special precautions are necessary. The metal of the 
furnace charge is earthed by electrodes connected at 
the bottom of the charge, and the furnace coils are 
connected to the mains supply but are unearthed. A relay 
is connected by a detection circuit which itself is earthed 
to the coils. The object is to prevent dangerous break- 
through of hot metal through the furnace lining, the earth 
detection circuit giving a continuous review of the 
conditions for the furnace lining. When leakage current 
attains a certain set maximum it becomes necessary to 
take the furance out of service and to re-line. 

7 EMERGENCY/STANDBY POWER SUPPLIES 
7.1 The provisions of Part 2 of the Code shall apply. 

8 SYSTEM PROTECTION 
8.1 Protection of Circuits 

8.1.1 Appropriate protection shall be provided at 
switchboards and distribution boards for all circuits 
and sub-circuits against overcurrent and earth faults, 
and the protective apparatus shall be capable of 



interrupting any short-circuit current that may occur, 
without danger. The ratings and settings of fuses and 
the protective devices shall be coordinated so as to 
afford selectivity in operation where necessary. 

8.1.2 Where circuit-breakers are used for protection 
of a main circuit and of the sub-circuits derived 
therefrom, discrimination in operation may be achieved 
by adjusting the protective devices of the sub- main 
circuit-breakers to operate at lower current settings and 
shorter time-lag than the main circuit-breaker. 

8.1.3 Where HRC type fuses are used for backup 
protection of circuit-breakers, or where HRC fuses are 
used for protection of main circuits and circuit-breakers 
for the protection of sub-circuits derived therefrom, in 
the event of short circuits exceeding the breaking 
capacity of the circuit-breakers, the HRC fuses shall 
operate earlier than the circuit-breakers; but for smaller 
overloads within the breaking capacity of the circuit- 
breakers, the circuit-breakers shall operate earlier than 
the HRC fuse. 

8.1.4 If rewirable type fuses are used to protect 
sub-circuits derived form a main circuit protected by 
HRC type fuses, the main circuit fuse shall normally 
blow in the event of a short-circuit or earth fault 
occurring on a sub-circuit, although discrimination may 
be achieved in respect of overload currents. The use of 
rewirable fuses is restricted to the circuits with short- 
circuit level of 4 kA; for higher level either cartridge 
or HRC fuses shall be used. 

8.1.5 Provision shall also be made for control of general 
lighting and other emergency services through separate 
main circuits and distribution boards from the power 
circuits. 

8.1.6 If necessary, independent source of supply for 
emergency service in particular installations may be 
provided. 

8.1.7 Search suppressors shall be provided at the 
incomers of the sub distribution boards as considered 
necessary. 

8.1.8 Wherever necessary to control the harmonics 
within permissible limits, passive/active filters may be 
used. 

8.2 Fire-safety Requirements 

8.2.1 Besides fire fighting equipment, the fire detection 
and extinguishing systems, as recommended in Part 4 
of SP 7 shall be followed. 

8.2.2 Reference is also drawn to IS 1646 regarding 
rules and regulations relating to electrical installations 
from the point of fire safety. Annex D covers specific 
requirements for fire safety for representative 
industries. 



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9 BUILDING SERVICES 

9.1 Lighting 

9.1.0 Industrial lighting encompasses seeing tasks, 
operating conditions and economy. With each of the 
various visual task conditions, lighting should be 
suitable for adequate visibility. Physical hazards exist 
in many manufacturing processes, therefore, lighting 
contribute to the utmost as a safety factor in preventing 
accidents. The speed of many manufacturing 
operations might also be hampered due to poor lighting. 
The general considerations for design of lighting in 
industrial areas are enumerated in IS 6665 (see also 
SP72). 

9.1.1 Equipment for Lighting 

The choice of light sources and luminaries shall be 
governed by the guidelines given in IS 6665. The 
recommended values of illumination and limiting 
values of glare index are given in Annex E for guidance. 

.9.2 Air-conditioning, Heating and Ventilation 

9.2.1 The electrical installation meant for the services 
such as air-conditioning heating and ventilation in 
industrial buildings shall conform to the requirements 
given in Part 1/Sec 1 1 of the Code. The specific needs 
of individual locations requiring these services in each 
factory shall be ascertained in consultation with the 
concerned personnel before designing the electrical 
system. Reference should be made to the guidelines 
given in SP 7. 

9.3 Lifts 

9.3.1 The general rules laid down in Part 1/Section 1 1 
of the Code shall apply regarding lift installations. 
However, the design of lifts in industrial buildings shall 
take into account the following requirements: 

a) Occupant load — The occupant load ex- 
pressed in terms of gross area in m 2 /person 
shall be 10 for industrial buildings. 

b) Car-speed for goods lifts — These shall be as 
follows: 

1) Normal load carrying lifts — 2-2.5 m/s 



2) Lifts serving many floors — 1 m/s 

9.3.2 The location of lifts in factories, warehouses and 
similar buildings should be planned to suit the 
progressive movement of goods through the buildings 
having regard to the nature of processes carried out, 
position of loading platform, railway slidings, etc. The 
placing of a lift in a fume or dust laden atmosphere, or 
where it may be exposed to extreme temperatures shall 
be avoided. Where it is impossible to avoid extreme 
environmental conditions. The selection of electrical 
equipment shall be such that they are suitable to meet 
the conditions involved. 

10 MISCELLANEOUS/SPECIAL PROVISIONS 

10.1 Control of Static Electricity 

See IS 7689 regarding recommendations for controlling 
static electricity generated incidentally by processes 
in industries which may pose a hazard or 
inconvenience. Specific control methods are also given 
for some industries therein. 

10.2 Safety in Electro-Heat Installations 

Industrial process include in many instances, electro- 
heat installations such as; 



a) 
b) 

c) 

d) 



e) 
f) 



Arc furnaces; 

Induction furnaces; 

Appliances for direct and indirect resistance 

heating; 

Medium and high frequency induction 

heating, radio frequency heating and 

dielectric heating appliances; 

Infra-red radiatum heating appliances; and 

Microwave heating. 



For safety requirements in such electro-heat 
installations reference shall be made to IS 9080 (Parts 2 
and 4) and IS/IEC 60519 (Parts 1, 3, 5 and 9). 

103 POWER FACTOR COMPENSATION 

10,3.1 The provisions of Part 1/Section 17 of the Code 
shall apply. For specific guidance for installations 
covered by this Part (see Annex F). 



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ANNEX A - 






(Clause 2) 




IS No. 


Title 


IS No. 


732: 


1989 


Code of practice for electrical 
wiring installations 


7689 : 1989 


1646 


: 1997 


Code of practice for fire safety of 
buildings (general): Electrical 
installations 


9109 : 2000 


2726 


: 1988 


Code of practice for fire safety of 








industrial buildings: Cotton 


9080 (Part 2/ 






ginning and pressing (including 


Sec 2) : 1980 






cotton seed delintering) factories 




3058 


: 1990 


Code of practice for fire safety of 
industrial buildings: Viscose 
rayon yarn and/or staple fibre 








plants 


9080 (Part 2/ 


3079 


: 1990 


Code of practice for fire safety of 
industrial buildings: Cotton textile 
mills 


Sec 4): 1981 


3594 


: 1991 


Code of practice for fire safety of 








industrial buildings: General 


IS/IEC 60519-1 






storage and warehousing 


1984 
IS/IEC 60519-3 






including cold storage 


3595 


:2002 


Code of practice for fire safety of 
industrial buildings : Coal 
pulverizers and associated 
equipments 


1988 


3836: 


:2000 


Fire safety of industrial buildings 


IS/IEC 60519-5 






— Jute mills — Code of practice 


1980 


4226: 


: 1988 


Code of practice for fire safety of 








industrial building: Aluminium/ 


IS/IEC 60519-9 






Magnesium powder factories 


1987 


4886: 


: 1991 


Code of practice for fire safety of 
industrial buildings: Tea factories 




6329: 


:2000 


Code of practice for fire safety of 


IS/IEC 60947-1 






industrial buildings — Saw mills 


2004 






and wood works 




6665: 


: 1972 


Code of practice for industrial 


SP 7 : 2005 






lighting 


SP 72: 2010 



Title 

Guide for the control of 
undesirable static electricity 
Fire safety of industrial buildings 
— Pradio frequency paint and 
varnish factories — Code of 
practice 

Safety requirements in electro- 
heat installations: Part 2 Particular 
requirements for resistance 
heating equipment, Section 2 
Protection in indirect resistance 
heating installations 
Safety requirements in electro- 
heat installations: Part 2 Particular 
requirements for resistance heating 
equipment, Section 4 Protection in 
installations used for drying 
varnishes and other similar products 
Safety in electroheat installation: 
Part 1 General requirements 
Safety in electroheat installations: 
Part 3 Particular requirements for 
induction and conduction heating 
and induction melting 
installations 

Safety in electroheat installation: 
Part 5 Specification for safety in 
plasma installation 
Safety in electroheat installations: 
Part 9 Particular requirements for 
high-frequency dielectric heating 
installations 

Specification for low-voltage 
switchgearandcontrolgear: Part 1 
General rules 

National Building Code of India 
National Lighting Code 



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ANNEX B 
(Clause 4.1.2) 

EXAMPLES OF INDUSTRIES BASED ON FIRE-SAFETY 



B-l The following is a representative list of industries 
classified according to the degree of fire hazard 
enumerated in 4.1.1: 

a) Low Hazard Industries 

Abrasive manufacturing premises 
Aerated water factories 
Agarbatti manufacturing premises 
Aluminium copper and zinc factories 
Asbestos steam packing and lagging 

manufacturers 
Battery manufacturers 
Bone mills 
Breweries 
Canning factories 
Carbon dioxide plants 
Cardamom factories 
Cement factories 
Cement and/or asbestos or concrete products 

manufacturing premises 
Ceramic and crockery factories 
Clay works 

Clock and watch manufacturing premises 
Confectionery manufacturers 
Electric generating houses 
Electric lamps and fluorescent tube 

manufacturers 
Electronic goods manufacturing premises 
Electroplating workshops 
Engineering workshops 
Fruit products and condiment factories 
Gold thread factories/gilding factories 
Glass factories 
Gum and glue factories 
Ice candy and ice cream manufacturing 

premises 
Ice factories 

Ink factories (excluding printing inks) 
Milk pasteurising plants and dairy farms 
Mica products manufacturing premises 
Potteries/tiles and brick works 
Rice mills 

Refractories works and firebrick kilns 
Salt crushing factories and refineries 
Silicate (other than sodium silicate) factories 
Soap and detergent factories 



Sugar candy manufacturers 

Sugar factories 

Tanneries 

Tea colouring factories 

Umbrella factories 

Vermicelli factories 

Wire drawing works 

b) Moderate Hazard 

Aeronaut/betelnut factories 

Atta and cereal grinding premises 

Bakeries and/or biscuit factories 

Beedi factories 

Book binders and paper cutting premises 

Book sellers and stationers' shops 

Boot and shoe factories and other leather 

goods factories 
Boat builders and ship repairing docks 
Button factories 
Candle works 

Canvas sheet manufacturers 
Cardboard box manufacturers 
Carbon paper manufacturing premises 
Carpet and durries factories 
Carpenter's workshops 
Camphor boiling premises 
Cashew nut factories (using open fire) 
Cloth processing works 
Coffee curing premises 
Coffee roasting and grinding works 
Colour/dyes mixing and/or blending factories 
Coir factories 
Cork factories 
Cork stopper and other cork products 

manufacturing premises 
Collieries 

Chemical manufacturers 
Cotton mills 

Dyeing and dry cleaning works 
Electric wire and cable manufacturing 

premises 
Enamel factories 
Essential oil distillation plants 
Flour mills 
Garment makers 



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Ghee manufacturing premises 
Ginning and pressing factories 
Grains and/or seeds disintegrating factories 
Grease manufacturing works 
Gunning and pressing factories 
Hat and topee factories 
Hosiery factories 

Incandescent gas mantle manufacturers 
Jute mills and jute presses 
Mineral oil blending and processing works 
Mutton tallow manufacturers 
Manure and/or fertilizer works (blending, 
mixing and granulating only) 

Mattresses and pillow making premises 

Oxygen plants 

Paper mills 

Pencil factories 

Plastic goods manufacturers 

Printing press premises 

Pulverizing and crushing mills (hazardous 

materials) 
Rice mills 
Rope factories 

Rubber goods manufacturers 
Shellac factories 
Spray painting works 
Starch factories 

Synthetic fibre manufacturing premises 
Tea factories 
Thermal power stations 
Tobacco (chewing), zarda, kimam and pan 

masala making premises 
Tobacco grinding and crushing and snuff 

manufacturing premises 
Tobacco curing and redrying factories 
Tobacco pressing works 
Upholsterers 
Weaving factories 
Woollen mills 

Wool cleaning/pressing factories 
Yarn gassing plants. 

c) High Hazard 
Acetylene plants 



Alcohol distillers 

Aluminium and magnesium powder plants 

Bituminished paper/hessian cloth 

manufacturing premises 

Bobbin factories 

Cinematograph film production studies 

Calcium carbide plants 

Cotton waste factories 

Coal/coke/charcoal ball and briquettes 

factories 
Celluloid goods manufacturers 
Cigarette filter manufacturers 
Cotton seed cleaning or deliniting premises 
Duplicating and stencil paper manufacturers 
Fertilizer plants 
Explosive manufacturers 
Fireworks factories 
Foam plastics and foam rubber goods 

manufacturers 

Grass, hay, fodder and bhoosa (chaff) pressing 

factories 
Match factories 
Oil mills 

Oil extraction plants 
Oil and leather cloth factories 
Paint (including nitrocellulose paints) and 

varnish factories 
Petrochemical plants 
Plywood factories 
Printing ink manufacturers 
Resin and lamp black manufacturers 
Rubber substitute manufacturers 
Surgical cotton manufacturers 
Tar distilleries 

Tar felt manufacturing premises 
Tarpauplin and canvas proofing factories 
Timber and woodworkers' premises 
Tin printers (where more than 50 percent of 

floor area is occupied as engineering 

workshop this may be taken as moderate 

hazard risk) 
Terpentino distilleries 
Tyre retreading and resoling factories 
Woodmeal manufacturers 



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ANNEX C 
(Clause 6.5) 

SELECTION OF WIRING SYSTEMS 



C-l WIRING SYSTEMS FOR GENERAL 

APPLICATION 

a) Bare solid or tubular conductors supported on 
insulators in metal or incombustible structural 
ducts or chases (main connections). 

b) Tough rubber-sheathed or PVC-sheathed 
cables protected as necessary against 
mechanical damage, say, buried in plaster or 
installed in concrete ducts. 

NOTE — Polythene-insulated PVC-sheathed cable 
provides an alternative having the advantage of high 
insulation-resistance. 

c) Elastomer-insulated braided and compounded 
or PVC-insulated cable installed in heavy- 
gauge screwed conduit. 

NOTE — The use of galvanized conduit and PVC- 
insulated cable is to be preferred where the situation 
may be damp or long life is required. 

d) Elastomer-insulated braided and compounded 
or PVC-insulated cable installed in light- 
gauge steel conduit with lug grip. 

e) Elastomer-insulated braided and compounded 
or PVC-insulated cable installed in PVC or 
other insulated conduit and provided with a 
bare copper or copper-alloy earth-continuity 
conductor as necessary. 

f) Grid suspension wiring system comprising 
elastomer-insulated or PVC insulated cables 
laid around a galvanized steel catenary wire, 
braided overall or otherwise protected to 
withstand corrosive conditions where 
necessary. 

g) Elastomer-insulated braided and compounded 
or PVC-insulated cable installed in metal 
trunking or ducts. 

NOTE — Incombustible insulated trunking and ducts 
provide an alternative and where these are used a bare 
copper or copper-alloy earth-continuity conductor may 
be required. 

h) Elastomer-insulated braided and compounded 
or PVC-insulated cable installed on cleats, 
with appropriate protection where cable 
passes through floors or walls. 

j) Elastomer-insulated lead-alloy-sheathed 
cables incorporating an earth continuity 
conductor, or elastomer-insulated aluminium- 
sheathed cable, protected as necessary against 
mechanical damage and corrosion. 
NOTE — Where a lead-sheathed cable has plumbed 
joints a separate earth-continuity conductor may not be 
required. 

k) Mineral-insulated metal-sheathed cable with 



or without protective sheathing with suitable 
watertight glands. 

C-2 ADDITIONAL WIRING SYSTEMS 
PARTICULARLY SUITABLE FOR USE IN 
FACTORIES AND THE LIKE 

n) PVC-insulated and steel tape or wire 

armoured and PVC-sheathed cable buried 

directly in the ground or used in special 

conditions, 
p) PVC-insulated steel tape or wire armoured 

and PVC-sheathed cable with cleat or hook 

suspensions, 
q) PVC-insulated and PVC-sheathed cable, 

installed in underground earthenware ducts 

or metal pipes. 

r) PVC-insulated and PVC-sheathed cable, 
mounted on porcelain or hardwood cleats or 
in trenches or ducts, and so installed as to be 
protected against mechanical damage. 

s) Tough rubber-sheathed or PVC-sheathed 
cable mounted on insulating non-hygro- 
scopic cleats affixed to treated, teak 
battens by screws of corrosion-resisting 
material, such as Monel metal or phosphor- 
bronze. 

t) Elastomer-insulated braided and compounded 
or PVC-insulated cable installed in galvanized 
solid-drawn screwed conduit with flameproof 
couplings and inspection fittings. 

u) Varnished-cambric insulated, lead-alloy or 
aluminium-sheathed cable. 

v) Elastomer-insulated, tough rubber- sheathed 
cable, steel wire armoured. 

NOTE — Varnished cambric insulated cables without 
metal sheath should be used only for short connections 
on switchboards and the like in dry situations. 

w) Cross-linked polyethylene insulated 
thermoplastic sheathed, armoured cable. 

C-3 SELECTION OF WIRING SYSTEMS FOR 
FACTORIES 

C-3.1 Wiring systems suitable for installations in 
different categories of factories are given in Table 3. 

C-4 SPECIAL RESTRICTIONS 

C-4.1 Even though guidance may be taken from the 
selection chart (see Table 3) for wiring systems, the 
following restrictions to their use apply: 



286 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



Wiring 


Restrictions 


Wiring 


Restrictions 


System (see 




System (see 




C-l, C-2) 




C-l, C-2) 




(1) 


(2) 


(1) 


(2) 



b) and g) If the ducts are in the form of under 
floor trenches then the following 
provisions should be observed: 

1) Cables shall preferably be so 
mounted on suitably earth cracks 
or other supports and has to be at 
least 75 mm above the bottom. 

2) Top of trenches shall be covered 
with chequered plates or concrete 
slabs, 

3) In case of long trenches, it is 
recommended that trenches of 
more than 1 000 cm 2 cross- 
sectional area be divided by 
incombustible barriers at 
intervals not exceeding 45 m. 
The barriers shall be at least 
50 mm in thickness and of the 
same height as of cable trench. 
The cables shall be carried 
through holes in the barriers, 
which shall be made good 
thereof to prevent the passage of 
fire beyond the barriers, 

4) The combined cross- sectional 
area of all conductors or cables 
shall not as far as possible exceed 
40 percent of the internal cross- 
sectional area of the trench, and 

5) The cable trenches shall be kept 
free from accumulation of water, 
dusts and waste materials. 

c) Trunking or ducting systems for cables 

above ground shall not be used where: 

1) they are exposed to physical 
damage, 

2) they are exposed to corrosive 
vapours. 

3) the atmosphere is likely to 
contain flammable gases or 
vapours, 

4) the wet processes are carried out, 
or 

5) in concealed spaces. 
Ordinary steel conduits shall not be 
permitted in areas where flammable 
vapour may be present, unless it is of 
type conforming with wiring system (t) 
and shall not be permitted in locations: 
1) where wiring height is less than 

2.5 m above working floor level, 
unless protected against 
mechanical damage, 

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



2) 



d) 



e) 



h) and s) 



J) 

m), n), p) 

and v) 



3) 

4) 
5) 



they are exposed to corrosive 

vapours. 

where atmosphere is likely to 

contain flammable gases or 

vapours, 

where wet processes are carried 

out, or 

in concealed spaces. 
Ordinary steel conduits shall not be 
permitted in areas where flammable 
vapour may be present, unless it is of 
type conforming with wiring system (t) 
and shall not be permitted in locations: 

1) where wiring height is less than 
2.5 m above working floor level, 
unless protected against 
mechanical damage, 

2) where ambient temperature is 
likely to be above 55°C at 
sometime or other during the year, 

3) in concealed spaces of 
combustible construction, 

4) where atmosphere is likely to 
contain flammable gases or 
vapours, or 

5) where conductor operates at 
voltage above 650 V. 

It shall be permitted only where voltage 
is below 650 V and in locations where 
the atmosphere is unlikely to contain 
any flammable vapours or gases. 
Same as in case of wiring system (d). 
This system shall not be permitted in 
locations: 

1) where exposed to severe physical 
damage, 

2) where exposed to corrosive 
vapours, 

3) where wet processes are carried 
out, or 

4) in concealed places. 

These systems should only be 
permitted for voltage below 250 V and 
that too only if use of such system is 
essential. 

Same as in case of wiring system (d). 
Armoured cables shall not be permitted 
in following locations unless the cable 
is of PVC-sheathed type, and shall not 
be permitted in locations exposed to 
corrosive fumes or vapour; and battery 
rooms. 

287 



SP 30: 2011 



Table 3 Selection Chart for Wiring Systems for Installations in Factories 
(Clauses C-3.1 and C-4.1) 



SI No. 


Section of Installation 


Category of Factory 








Average Factory 


Heavy Industry Light Industry 


Chemical Industry 


Factories 
Involving 
Fire Risk 

(11) 


0) 


r" -\ r- —>> r "\ r 

1st 2nd 1st 2nd 1st 2nd 

Choice Choice Choice Choice Choice Choice 

(2) (3) (4) (5) (6) (7) (8) 


1st 2nd 

Choice Choice 

(9) (10) 



i) Main distribution at 
medium or low voltage 



k 
w 
n 



k 
w 
n 
r 



k 
w 
n 



ii) 



Sub-main distribution to 
local distribution boards 



iii) Sub-circuit wiring 



c 
f 
k 
w 
P 

V 

c 

f 
g 

k 



c 
f 
k 
w 

P 
r 

b 
h 
J 



g 
k 
w 
P 

V 



w 

q 

r 



NOTE — For description of a, b, c w, see C-l and C-2. 



ANNEX D 
(Clause 8.2.2) 

REQUIREMENTS FOR FIRE SAFETY IN SPECIFIC INDUSTRIES 



Type of Industry 


Ref.IS 


Motors 


Other Equipment 


Fittings 


Miscellaneous 


(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


Jute spinning and 


3836 


All motors shall be 


All equipment shall 


Lighting fittings 


Supply shall be at < 


weaving, jute rope, 




totally enclosed type 


be metal clad, dust- 


shall be dust-tight 


250 V in jute 


carpet making factories 




and in wet locations 
shall be drip-proof 


tight 




godowns 


Cotton ginning cotton 


2726 




All equipment shall 






seed delintering and 






be metal clad, dust- 






pressing factories 






tight 






Plants making viscose 


3058 




All equipment in the 


Vapour-proof 


All current carrying 


rayon yarn or staple 






Xanthation 


lighting fittings in 


parts, contacts liable 


fibre or both 






disulphide plant 


areas where 


for corrosion shall 








shall comply with 


corrosive gases are 


be cadmium plated 








Part 8 of the Code 


evolved 





288 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



Type of Industry 


Ref.lS 


Motors 


Other Equipment 


Fittings 


Miscellaneous 


(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


Textile mills using 


3079 


Totally enclosed 


Metal clad and dust- 


Dust-tight lighting 


Machines for 


cotton, cotton waste 




type, the cooling air 


tight. Equipment 


fittings at willowing, 


singeing yarn shall 


regenerated cellulose, 




for variable speed 


shall be flameproof 


lap breaking, waste 


be protected to 


man-made fibres or 




motor taken from 


in gas singeing 


opening, mixing, 


ensure that heating 


any grouping of these 




outside the building 


rooms. Stop motion 


blow and raising 


elements are not 








devices provided on 


rooms 


switched on while 








frames shall be dust- 




yarn is stationary 








tight 






Places where paints 


9109 


— 


— 


Wiring in steel 


Provisions shall be 


and varnishes are 








conduits. Lighting 


made for switching 


stored or processed 








fittings of enclosed 
type 


off the whole factory 
at more than one 
control point 


Factories where 


4226 


Motors shall be 


All equipment of 


Wiring in steel 


Provisions shall be 


powders of aluminium, 




flameproof dust- 


the enclosed type 


conduits. Enclosed 


made for switching 


magnesium and their 




protected (see Part 7 




lighting fittings 


off the whole factory 


alloys are processed or 




of the Code) 






at more than one 


used 










control point 


Coal pulverizing mills, 


3595 


Totally enclosed, 




Lighting fittings 


Use of flexible 


as also equipment 




flameproof, dust- 




shall be dust-tight. 


cables to be kept to 


therein for power 




proof (see Part 7 of 




Only conduits; 


the minimum 


generation cole or 




the Code) 




armoured or mineral 




briquette making 








insulated type of 
wiring 




Tea factories 


4886 


Where practicable, 
totally enclosed 
type 






Fan motors of 
dryers and 
withering troughs 
and other control 
equipment shall be 
dust proof tape 


Godowns, ware-houses, 


3594 


Driving motors for 


All switchgear 


Screwed steel 


All control 


outdoor storage sites 




overhead cranes 


equipment metal 


conduits mineral 


equipment switches, 


forming part of 




totally enclosed 


enclosed. For mains 


insulated, copper or 


etc., outside 


industrial complexes or 






operated electrical 


aluminium sheathed 


godown where 


others; cold storage 






stackers, switch and 


cable. Lighting 


fibrous goods, 


buildings 






socket shall be 


fittings to be 


flammable liquids, 








water-tight. Flexible 


positioned not 


nitro-cellulose, fire 








connection to the 


below 45 cm below 


works or explosives 








stacker through 


roof A clearance of 


are stored 








rubber compound 


not less than 75 cm 










sheathed trailing 


to be provided from 










cable with hard cord 


highest stacking 










braiding 


level. Flexible 
lighting pendants or 
portable lamps not 
allowed 




Saw mills, furniture 


6329 


Motors shall be 


All equipment shall 




Electrical heaters 


factories, coach and 




totally enclosed or 


be dust-tight and 




shall be metal cases, 


body build works, up- 




pipe ventilated 


where spray painting 




totally enclosed, 


holsteries and other 






is done shall comply 




immersion type or 


wood working shops. 






with Part 7 of the 




totally enclosed low 


Plywood hard-wood, 






Code 




temperature type 


wood wool, insulation 










with external 


boards, wood flour, etc 










surface below 92°C 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



289 



SP 30 : 2011 



ANNEX E 
(Clause 9.1.1) 

RECOMMENDED VALUES OF ILLUMINATION AND LIMITING VALUES OF 
GLARE INDEX — INDUSTRIAL BUILDINGS 



SI No. Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 



150 
100 
100 

20 



i) General factor areas: 

a) Canteens 

b) Cloakrooms 

c) Entrances, corridors, stairs 
ii) Factory outdoor areas: 

Stockyards, main entrances, exit roads, car parks, internal factory roads 
iii) Aircraft factories and maintenance hangers: 

a) Stock parts productions 

b) Drilling, riveting, screw fastening, sheet aluminium layout and 
template work, wing sections, cowling welding, sub-assembly, 
final assembly, inspection 

c) Maintenance and repairs (Hangers) 
iv) Assembly shops: 

a) Rough work, for example, frame assembly, assembly of heavy 
machinery 

b) Medium work, for example, machined parts, engine assembly, 
vehicle body assembly 

c) Fine work, for example, radio and telephone equipment, typewriter 
and office machinery assembly 

d) Very fine work, for example, assembly of very small precision 
mechanisms, instruments 

v) Bakeries: 

a) Mixing and make-up rooms, oven rooms, wrapping rooms 

b) Decorating and icing 
vi) Boiler houses (industrial): 

a) Coal and ash handling 

b) Boiler rooms: 

1) Boiler fronts and operating areas 

2) Other areas 

c) Outdoor plants: 

1) Catwalks 

2) Platforms 
vii) Bookbinding: 

a) Pasting, punching and stitching 

b) Binding and folding; miscellaneous machines 

c) Finishing, blocking and in laying 
viii) Boot and shoe factories: 

a) Sorting and grading 

b) Clicking and closing, preparatory operations 

c) Cutting table and presses, stitching 

d) Bottom stock preparation, lasting and bottoming, finishing 



450 


25 


300 


25 


300 


25 


150 


28 


300 


25 


700 


22 


1 500' > 


19 


150 


25 


200 


25 



100 



100 2) 


' — 


20 to 25 


— 


20 





50 


— 


200 


25 


300 


22 


300 


22 


1 000 3) 


19 


700 


22 


1000 


22 


700 


22 



290 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



150 


25 


200 


25 


Special lighting 


— 


450 


22 


300 


25 


200 


25 


300 


25 


450 


— 


200 


25 


450 


22 



SI No. Industrial Buildings and Processes Average Limiting Glare 

Illumination, lux Index 
(1) (2) (3) (4) 

e) Shoe rooms 700 22 

ix) Breweries and distilleries: 

a) General working areas 

b) Brewhouse, bottling and canning plants 

c) Bottle inspection 
x) Canning and preserving factories; 

a) Inspection of beans, rice, barley, etc 

b) Preparation: kettle areas, mechanical cleaning, dicing, trimming 

c) Canned and bottled goods: retorts 

d) High speed labelling lines 

e) Can inspection 
xi) Carpet factories: 

a) Winding, beaming 

b) Designing, Jacquard and cutting, setting pattern, tufting, topping, 
cutting, hemming, fringing 

c) Weaving, mending, inspection 450 22 
xii) Ceramics — See pottery and clay products 

xiii) Chemical works: 

a) Hand furnaces, boiling tanks, stationery driers, stationery or gravity 150 28 
crystalizers, mechanical driers, evaporators, filtration plants, 
mechanical crystallising bleaching, extractors, percolators, 
nitrators. electrolytic cells 

b) Controls, gauges, values, etc 100 — 

c) Control rooms: 

1) Vertical control panels 

2) Control desks 
xiv) Chocolate and confectionery factories: 

a) Mixing, blending, boiling 

b) Chocolate husking, winnowing, fat extraction, crushing and 
refining, feeding, bean cleaning, sorting, milling, cream making 

c) Hand decorating, inspection, wrapping, packing 300 22 
xv) Clothing factories: 

a) Matching-up 450 3) 19 

b) Cutting sewing: 

1) Light 

2) Medium 

3) Dark 

4) Pressing 

c) Inspection: 

1) Light 

2) Medium 

3) Dark 

d) Hand tailoring: 

1) Light 

2) Medium 

3) Dark 

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 291 



200-300 


19 


300 


19 


150 


28 


200 


25 



300 


22 


450 


22 


700 


22 


300 


22 


450 


19 


1000 


19 


1 500 


19 


450 


19 


1000 


19 


1500 


19 



SP 30 : 2011 



SI No. Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 



xvi) 


Collieries (surface buildings): 










a) 


Coal preparation plant: 
1) Working areas 




150 


_ 






2) Other areas 




100 


— 






3) Picking belts 




300 


— 






4) Winding houses 




150 


— 




b) 


Lamp rooms: 

1) Main areas 

2) Repair sections 

3) Weigh cabine 




100 
150 
150 


— 




c) 


Fan houses 




100 


— 


xvii) 


Dairies: 










a) 


General working areas 




200 2) 


25 




b) 


Bottle inspection 


Special lighting 


— 




c) 


Bottle filling 




450 


25 


xviii) 


Die sinking: 










a) 


General 




300 


— 




b) 


Fine 




1000 


19 


xix) 


Dye works: 










a) 


Reception, 'grey' perching 




700 


— 




b) 


Wet processes 




150 2 > 


28 




c) 


Dry processes 




200 2) 


28 




d) 


Dyers' offices 




700 3} 


19 




e) 


Final perching 




2 000 3) 


— 


xx) 


Electricity generating stations: Indoor locations 










a) 


Turbine halls 




200 


25 




b) 


Auxiliary equipment; battery rooms, blowers 
switchgear and transformer chambers 


auxiliary generators, 


100 


— 




c) 


Boiler houses (including operating floors) platforms, coal conveyors, 
pulverizers, feeders, precipitators, soot and slag blowers 


70-100 


— 




d) 


Boiler house and turbine house 




100 


— 




e) 


Basements 




70 


— 




f) 


Conveyor houses, conveyor gantries, junction 


towers 


70-100 


— 




g) 


Control rooms: 












1) Vertical control panels 




200-300 


19 






2) Control desks 




300 


19 






3) Rear of control panels 




150 


19 






4) Switch houses 




150 


25 




h) 


Nuclear reactors and steam, raising plants: 












1) Reactor areas, boilers, galleries 




150 


25 






2) Gas circulator days 




150 


25 






3) Reactor charge/discharge face 




200 


25 


xxi) 


Electricity generating stations: Outdoor locations 










a) 


Coal unloading areas 




20 


— 




b) 


Coal storage areas 




20 


— 



292 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



SI No. Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 





c) Conveyors 


50 


— 




d) Fuel oil delivery headers 


50 


— 




e) Oil storage tanks 


50 


— 




f) Catwalks 


50 


— 




g) Platforms, boiler and turbine decks 


50 


— 




h) Transformers and outdoor switchgear 


100 


— 


xxii) 


Engraving: 








a) Hand 


1000 


19 




b) Machine (see Die sinking) 


— 


— 


xxiii) 


Farm buildings (dairies) 








a) Boiler houses 


50 


— 




b) Milk rooms 


150 


25 




c) Washing and sterilizing rooms 


150 


25 




d) Stables 


50 


— 




e) Milking parlours 


150 


25 


xxiv) 


Flour mills: 








a) Roller, purifier, sifting and packing floors 


150 


25 




b) Wetting tables 


300 


25 


xxv) 


Forges: General 


150 


28 


xxvi) 


Foundries: 








a) Charging floors, tumbling cleaning, pouring, shaking out, rough 


150 


25 




moulding and rough core making 








b) Fine moulding and core making, inspection 


300 


25 


xxvii) 


Garages: 








a) Parking areas (interior) 


70 


28 




b) Washing and polishing, greasing, general servicing, pits 


150 


28 




c) Repairs 


300 


25 


xxviii 


) Gas works: 








a) Retort houses, oil gas plants, water gas plants, purifiers, coke 


30-50 4) 


28 




screening and coke handling plants (indoor) 








b) Governor, meter, compressor, booster and exhauster houses 


100 


25 




c) Open type plants: 




— 




1) Catwalks 


20 4) 


— 




2) Platforms 


50 4) 


— 


xxix) 


Gauge and tool rooms: General 


700 5) 


19 


xxx) 


Glass works and processes: 








a) Furnace rooms, bending, annealing lehrs 


100 


28 




b) Mixing rooms, forming (blowing, drawing, pressing, rolling) 


150 


28 




c) Cutting to size, grinding, polishing, toughening 


200 


25 




d) Finishing (bevelling, decorating, etching, silvering) 


300 


22 




e) Brilliant cutting 


700 


19 




f) Inspection: 








1) General 


200 


19 




2) Fine 


700 


19 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



293 



SP 30 : 2011 



SI No. Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 



300 


22 


450 


22 


700 


22 



300 


22 


450 


22 


700 


22 



xxxi) Glove making: 

a) Pressing, knitting, sorting, cutting 300 22 

b) Sewing: 

1) Light 

2) Medium 

3) Dark 
xxxii) Hat making 

a) Stiffening, braiding, cleaning, refining forming, sizing, 150 22 
pouncing, flanging, finishing ironing 

b) Sewing: 

1) Light 

2) Medium 

3) Dark 
xxxiii) Hosiery and knitwear: 

a) Circular and flat knitting machines universal winders, cutting 300 22 
out, folding and pressing 

b) Lock stitch and overlooking machines: 

1) Light 

2) Medium 

3) Dark 

c) Mending 

d) Examining and hand finishing, light, medium, dark 

e) Linking or running-on 
xxxiv) Inspection shops (Engineering) 

a) Rough work, for example, counting, rough checking of stock 
parts, etc. 

b) Medium work, for example, 'Go' and 'No-go' gauges, 
sub-assemblies 

c) Fine work, for example, radio and telecommunication equipment, 
calibrated scales, precision mechanisms, instruments 

d) Very fine work, for example, gauging and inspection of small 
intricate parts 

e) Minute work, for example, very small instruments 
xxxv) Iron and steel works 

a) Marshalling and outdoor stockyards 

b) Stairs, gangways, basements, quarries, loading docks 

c) Slab yards' melting shops, ingot stripping soaking pits, blast 
furnace working areas, picking and cleaning lines, mechanical 
plants, pump houses 

d) Mould preparation, rolling and wire mills, mills motors rooms, 
power blower houses 

e) Slab inspection and conditioning, cold strip mills, sheet and plate 
finishing, tinning, galvanizing, machine and roll shops 

f) Plate inspection 

g) Tinplate inspection 



300 


22 


450 


22 


700 


22 


1500 


19 


700 


19 


450 


19 


150 


28 


300 


25 


700 


22 


1500 


19 


3 000 2 > 


19 


10-20 





100 


— 


100 


28 


150 


28 


200 


28 


300 


— - 


;ial lighting 


— 



294 



NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



SI No. Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 



b) 



xxxviii) 



a) 
b) 
c) 



xl) 



xli) 



xlii) 



xliii) 



xliv) 



xlv) 



b) 



c) 



700" 


19 


3 000" 


10 


1 500 3 > 


— 


300 


19 


450 


19 


200 


25 


200 


25 


300 


25 


150 


28 


200 


28 


450 


22 


700 


22 


1 000 3) 


19 


150 


28 


300 


25 



xxxvi) Jewellery and watchmaking 

a) Fine processes 

b) Minute processes 

c) Gem cutting, polishing, setting 
xxx vii) Laboratories and test rooms 

a) General laboratories, balance rooms 
Electrical and instrument laboratories 
Laundries and drycleaning works 

Receiving, sorting, washing, drying, ironing (calendering), despatch 
Drycleaning, bulk machine work 

Fine hand ironing, pressing, inspection mending, spotting 
xxxix) Leather dressing 

a) Vats, cleaning, tanning, stretching, cutting, fleshing and stuffing 

b) Finishing, staking, splitting and scrafing 
Leather working 

a) Pressing and glazing 

b) Cutting, scarfing, sewing 

c) Grading and matching 
Machine and fitting shops 
a) Rough bench and machine work 

Medium bench and machine work, ordinary automatic machines, 
rough grinding, medium buffing and polishing 
Fine bench and machine work, fine automatic machines, medium 
grinding fine buffing and polishing 
Motor vehicle plants 

a) General sub-assemblies, chassis assembly, car assembly 

b) Final inspection 

c) Trim shops, body sub-assemblies, body assembly 

d) Spray booths 
Paint works 

a) General automatic processes 

b) Special batch mixing 

c) Colour matching 
Paint shops and spraying booths: 

a) Dipping, firing rough spraying 

b) Rubbing, ordinary painting, spraying and finishing 

c) Fine painting, spraying and finishing 

d) Retouching and matching 
Paper- works: 
a) Paper and board making: 

1) Machine houses, calendering pulp mills, preparation plants, 
cutting, finishing, trimming 

2) Inspection and sorting (over hauling) 
Paper converting processes: 
1) Corrugated board, cartons, containers and paper sack 

manufacture, coating and laminating processes 



700 



b) 



22 



300 


25 


450 


25 


300 


25 


450 


— 


200 


25 


450 


22 


700 3 > 


19 


150 


25 


300 


25 


450 


25 


700 3 > 


19 


200 


25 


300 


22 


200 


25 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



295 



SP 30: 2011 



SI No, Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 



b) 

c) 



d) 



2) Associated printing 
xlvi) Pharmaceuticals and fine chemicals works: 
a) Raw material storage 

Control laboratories and testing 

Pharmaceuticals manufacturing: grinding, granulating, mixing 

and drying, tableting, sterilizing and washing, preparation of 

solutions and filling, labelling, capping, cartoning and wrapping, 

inspection 

Fine chemical manufacture: 

1 ) Plant processing 

2) Fine chemical finishing 
xlvii) Plastics works: 

a) Manufacture (see Chemical works) 

b) Processing: 

1) Calendering, extrusion 

2) Moulding-compression, injection 

3) Sheet fabrication: 
i) Shaping 

ii) Trimming, machining, polishing 
iii) Cementing 
xlviii) Plating shops: 

a) Vat and baths, filter pressing, kin rooms, moulding, pressing, 
cleaning, trimming, glazing, firing 

b) Enamelling, colouring, decorating 
xlix) Printing works: 

a) Type foundries: 

1) Matrix making, dressing type, hand and machine casting 

2) Front assembly, sorting 

b) Printing plants: 

1) Machine composition, imposing stones 

2) Presses 

3) Composing room 

4) Proof reading 

c) Electrotyping: 

1) Block-making, electroplating, washing, backing 

2) Moulding, finishing, routing 

d) Photo-engraving: 

1) Block-making, etching, masking 

2) Finishing, routing 

e) Colour printing: Inspection area 
1) Rubber processing: 

a) Fabric preparation creels 

b) Dipping, moulding, compounding calendars 

c) Tyre and tube making 



300 



200 
300 



25 



200 


28 


300 


19 


300 


25 



25 
25 



300 


25 


200 


25 


200 


25 


300 


25 


200 


25 


150 


28 


450 3 > 


19 


200 


25 


450 


22 


200 


25 


300 


25 


450 


19 


300 


19 


200 


25 


300 


25 


200 


25 


300 


25 


700 3) 


19 


200 


25 


150 


25 


200 


25 



296 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



SI No. Industrial Buildings and Processes 

(1) (2) 



Average Limiting Glare 
Illumination, lux Index 

(3) (4) 



li) Sheet metal works: 

a) Benchwork, scribing, pressing, punching shearing, stamping, 200 25 
spinning, folding 

b) Sheet inspection Special lighting 
lii) Soap factories: 

a) Kettle houses and ancillaries, glycerine evaporation and 
distillation, continuous indoor soap making, plants: 

1) General areas 

2) Control panels 

b) Batch or continuous soap cooling, cutting and drying, soap milling, 
plodding: 

1) General areas 

2) Control panels, key equipment 

c) Soap stamping, wrapping and packing, granules making, granules 
storage and handling, filling and packing granules: 

1) General areas 

2) Control panels, machines 

d) Edible products processing and packing 
liii) Structural steel fabrication plants: 

a) General 

b) Marking off 
liv) Textile mills (cotton or linen): 

a) Bale breaking, blowing, carding, roving, slubbing, spinning 
(ordinary counts), winding, heckling, spreading, cabling 

b) Warping, slashing, dressing and dyeing, doubling (fancy), spinning 
(fine counts) 

c) Healding (drawing-in) 700 

d) Weaving: 

1) Patterned cloths, fine counts dark 

2) Patterned cloths, fine counts light 

3) Plain 'grey' cloth 

e) Cloth inspection 
lv) Textile mills (silk or synthetics): 

a) Soaking, fugitive tinting, conditioning or setting of twist 

b) Spinning 

c) Winding, twisting, rewinding and coning, quality slashing: 

1) Light thread 

2) Dark thread 

d) Warping 

e) Healding (drawing-in) 

f) Weaving 

g) Inspection 
lvi) Textile mills (woollen): 

a) Scouring, carbonizing, teasing, preparing, raising, brushing, 150 25 

pressing, back-washing, gilling, crabbing and blowing 



150 


25 


200-300 


25 


150 


25 


200-300 


25 


150 


25 


200-300 


25 


200 


25 


150 


28 


300 


28 


150 


25 


200 


25 



700 


19 


300 


19 


200 


19 


700'> 


— 


200 


25 


450 


25 


200 


25 


300 


25 


300 


25 


700 


— 


700 


19 


L000 3 > 


19 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



297 



SP 30: 2011 



SI No. Industrial Buildings and Processes Average Limiting Glare 

Illumination, lux Index 
_0) (2) . (3) (4) 

b) Blending, carding, combing (white), tentering, drying, cropping 

c) Spinning, roving, winding, warping, combing (coloured), twisting 

d) Healding (drawing-in) 

e) Weaving: 

1) Fine worsteds 

2) Medium worsteds, fine woollens 

3) Heavy woollens 

f) Burling and mending 

g) Perching: 

1) Grey 

2) Final 
lvii) Textile mills (jute): 

a) Weaving, spinning, flat, jacquard carpet looms, cop winding 

b) Yarn calender 
lviii) Tobacco factories: All processes 

lix) Upholstering, furniture and vehicles 
lx) Warehouses and bulk stores: 

a) Large material, loading bays 

b) Small material, racks 

c) Packing and despatch 
Ixi) Welding and soldering: 

a) Gas and arc welding, rough spot welding 

b) Medium soldering, brazing and spot welding, for example, 
domestic hardware 

c) Fine soldering and spot welding, for example, instruments, radio 
set assembly 

d) Very fine soldering and spot welding, for example, radio valves 
lxii) Woodworking shops: 

a) Rough sawing and bench work 

b) Sizing, planning, rough sanding, medium machine, and bench 
work, gluing, veneering, cooperage 

c) Fine bench and machine work, fine sanding and finishing 300 22 



200 


25 


450 


25 


700 


— 


700 


19 


450 


19 


300 


19 


700 


19 


700 





2 000 3 > 


— 


200 


25 


150 


25 


300 3) 


22 


300 


22 


100 


28 


150 


25 


150 


25 


150 


28 


300 


25 


700 


22 


150 


19 


150 


22 


200 


22 



Optical aids should be used where necessary. 

2) Supplementary local lighting may be required for gauge glasses and instrument panels. 

3) Special attention should be paid to the colour quality of the light. 

4) Supplementary local lighting should be used at important points. 

53 Supplementary local lighting and optical aids should be used where necessary. 



298 NATIONAL ELECTRICAL CODE 



SP 30 : 2011 



ANNEX F 
(Clause 10) 

POWER FACTOR IN INDUSTRIAL INSTALLATIONS 



F-l The general guidelines for power factor compensation 
is given in Part 1/Sec 17 of the Code. For guidance, the 
natural power factor for some three phase electrical 



installations are given in Table 4. The recommended 
capacitor ratings at rated voltage, for direct connection 
to ac induction motor in industries are given in Table 5. 



Table 4 Power Factor for Three Phase Electrical Installations 

(Clause F-l) 



SI 


Type of Installation 


Natural Power 


SI 


Type of Installation 


Natural Power 


No. 




Factor 


No. 




Factor 


(1) 


(2) 
Cold storage and fisheries 


(3) 
0.76-0.80 


(1) 


(2) 


(3) 


i) 


xviii) 


Flour mills 


0.61 


ii) 


Cinemas 


0.78-0.80 


xix) 


Gas works 


0.87 


iii) 


Metal pressing 


0.57-0.72 


xx) 


Textile mills 


0.86 


iv) 


Confectionery 


0.77 


xxi) 


Oil mills 


0.51-0.59 


v) 


Dyeing and printing (textile) 


0.60-0.87 


xxii) 


Woolen mills 


0.70 


vi) 


Plastic moulding 


0.57-0.73 


xxiii) 


Potteries 


0.61 


vii) 


Film studios 


0.65 to 0.74 


xxiv) 


Cigarette manufacturing 


0.80 


viii) 


Newspapers 


0.58 


xxv) 


Cotton press 


0.63-0.68 


ix) 


Heavy engineering works 


0.48-0.75 


xxvi) 


Foundries 


0.59 


x) 


Rubber extrusion and moulding 


0.48 


xxvii) 


Tiles and mosaic 


0.61 


xi) 


Pharmaceuticals 


0.75-0.86 


xxviii) 


Structural engineering 


0.53-0.68 


xii) 


Oil and paint manufacturing 


0.51-0.69 


xxix) 


Chemicals 


0.72-0.87 


xiii) 


Silk mills 


0.58-0.68 


xxx) 


Municipal pumping stations 


0.65-0.75 


xiv) 


Biscuit factory 


0.60 


xxxi) 


Oil terminals 


0.64-0.83 


xv) 


Printing press 


0.65-0.75 


xxxii) 


Telephone exchange 


0.66-0.80 


xvi) 


Food products 


0.63 


xxxiii) 


Rolling mills 


0.72-0.60 


xvii) 


Laundries 


0.92 


xxxiv) 


Irrigation pumps 


0.52-0.70 



Table 5 Capacitor Ratings at Rated Voltage 

(Clause F-l) 



Rated Output 

of Motors 

kW 






Capacitor Rating in 


kVAR for Motor Speed 






3 000 


1500 


1000 


750 


600 


500 




rev/min 


rev/min 


rev/min 


rev/min 


rev/min 


rev/min 


(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


(7) 


2.25 


1 


1 


1.5 


2 


2.5 


2.5 


3.7 


2 


2 


2.5 


3.5 


4 


4 


5.7 


2.5 


3 


3.5 


4.5 


5 


5.5 


7.5 


3 


4 


4.5 


5.5. 


6 


6.5 


11.2 


4 


5 


6 


7.5 


8.5 


9 


15 


5 


6 


7 


9 


11 


12 


18.7 


6 


7 


9 


10.5 


13 


14.5 


22.5 


7 


8 


10 


12 


15 


17 


37 


11 


12.5 


16 


18 


23 


25 


57 


16 


17 


21 


23 


29 


32 


75 


21 


23 


26 


28 


35 


40 


102 


31 


33 


36 


38 


48 


55 


150 


40 


42 


45 


47 


60 


67 


187 


46 


50 


53 


55 


68 


76 



NOTES 

1 The reference to speed of motor has been made since the manufacturers provide information on that basis. 

2 The capacitive current supplied by condensers directly across induction motor terminals should not exceed the magnetizing current of 
the induction motors, to guard against excess transient torques and overvoltages. 

3 Should a consumer desire to improve the power factor beyond a value which is limited by considerations of magnetizing kVAR of the 
motor as stated in Note 2, then he may install the calculated capacitor kVAR as a separate circuit with its independent controlgear. 



PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 



299 



NATIONAL ELECTRICAL CODE 

PART 5 



SP 30: 2011 



PART 5 OUTOGO: I INSTALLATIONS 



FOREWORD 



As compared to the various types of indoor installations covered in other Parts of this Code, outdoor installations 
are distinct in nature by virtue of their being exposed to moderate to heavy environmental conditions. In addition, 
electric power in outdoor installations is normally utilized for specific purposes such as, lighting or for meeting 
the needs of heavy machinery (example, open cast mines). In the case of the latter, the duties would be more 
onerous than those normally encountered in indoor situations, thereby calling for special considerations in their 
design. 

Keeping the above in view, Part 5 of this Code deals with installations erected outdoor. Some outdoor installations 
are erected to serve for a small duration of time after which they are meant to be dismantled. Such installations 
are called temporary installation. For convenience, and keeping other aspects of safety provisions in view, this 
duration is defined as not exceeding six months. Permanent outdoor installations are those which are generally in 
use for longer periods of time. This Part 5 of this Code basically deals with these two types of outdoor installations. 

Part 5 consists of the following Sections: 

Section 1 Public Lighting Installations 
Section 2 Temporary Outdoor Installations 
Section 3 Permanent Outdoor Installations 

Even though installations for lighting of public thoroughfares are permanent in nature, they are dealt with separately 
in Section 1. 

It may, however, be noted that small outdoor locations around building installations (example, gardens around 
hotel installations or storage yards in industries) do not fall under the scope of Part 5 . For requirements pertaining 
to this, reference should be made to relevant parts of this Code. 

PART 5 OUTDOOR INSTALLATIONS 303 



SP 30 : 2011 



SECTION 1 PUBLIC LIGHTING INSTALLATIONS 



FOREWORD 

One of the most common forms of permanent outdoor 
installations is the public lighting installations intended 
for lighting of public thoroughfares. With the 
availability of variety of light sources for such 
installations and the need for proper illumination of a 
variety of traffic routes and city centres it has been 
found necessary to lay down guidelines for designing 
on efficient and economical lighting installation. 

This Section of this Code is intended to cover general 
principles governing the lighting of public 
thoroughfares and to lay down recommendations on 
the quantity and quality of lighting to be provided. The 
actual details of design would entirely depend on the 
local circumstances. 

The requirements given in this Section are, as far as 
practicable aligned with the recommendations of the 
International Commission on Illumination (CIE) 
modified to suit the local conditions and regulations. 

1 SCOPE 

1.1 This Part 5/Section 1 of the Code covers requirements 
of public lighting installations in order to provide 
guidance to those concerned with the preparation of 
public lighting schemes, their installation and 
maintenance (see also SP 72). 

1.2 This Section deals only with electric lighting 
sources and does not include gas or other types of 
lighting. 

1.3 This Section also does not cover exterior lighting 
installations, such as those which apply for parks, 
shopping enclaves, flood lighting of routes and 
structures of architectural importance, etc. 

2 REFERENCES 

This Part 5/Section 1 of the Code should be read in 
conjunction with the following Indian Standards: 

IS No. Title 

SP 72 : 2010 National Lighting Code 

1 885 (Part 16/ Electrotechnical vocabulary : Part 

Sec 2) : 1968 16 Lighting, Section 2 General 

illumination lighting fittings and 

lighting for traffic and signalling 

1944 (Parts 1 Code of practice for lighting of 

and 2): 1970 public thoroughfares: Part 1 

General principles; Part 2 

Lighting of main roads (first 

revision) 



IS No. 
1944 (Part 5): 1981 



1944 (Part 6): 1981 



Title 

Code of practice for lighting of 
public thoroughfares: Part 5 
Lighting of grade separated 
junctions, bridges and elevated 
road (Group D) 

Code of practice for lighting of 
public thoroughfares: Part 6 
Lighting of town and city centres 
and areas of civic importance 
(Group E) 



3 TERMINOLOGY 

3.0 For the purpose of this Section, the following terms 
together with those provided in IS 1885 (Part 16/ 
Section 2) shall apply. 

3.1 Terms Relating to Highways 

3.1.1 Highway — A way for the passage of vehicular 
traffic over which such traffic may lawfully pass. 

3.1.2 Layout — All those physical features of a highway 
other than the surfacing of the carriageway, which have 
to be taken into account in planning a lighting 
installation. 

3.1.3 Carriageway — That portion of a highway 
intended primarily for vehicular traffic. 

3.1.4 Dual Carriageway — A layout of the separated 
carriageways, each reserved for traffic in one direction 
only. 



3.1.5 Central Reserve - 
a dual carriageway. 



- A longitudinal space dividing 



3.1.6 Service Road — A subsidiary road between 
principle road and buildings or properties facing 
thereon or a parallel road to the principal road and 
giving access to the premises and connected only at 
selected points with the principle road". 

3.1.7 Cycle Track — A way or part of a highway for use 
by pedal cycles only. 

3.1.8 Footway — That portion of a road reserved 
exclusively for pedestrians. 

3.1.9 Verge — The unpaved area flanking a carriageway, 
forming part of the highway and substantially at the 
same level as the carriageway. 

3.1.10 Shoulder — A strip of highway adjacent to and 
level with the main carriageway to provide an 
opportunity for vehicles to leave the carriageway in an 
emergency. 



304 



NATIONAL ELECTRICAL CODE 



SP 30: 2011 



3.1.11 Refuge — A raised platform or a guarded area 
so sited in the carriageway as to divide the streams of 
traffic and to provide a safety area for pedestrians. 

3.1.12 Kerb — A border of stone, concrete or other 
rigid material formed at the edge of a carriageway. 

3.2 Terms Relating to Lighting Installation 

3.2.1 Lighting Installation — The whole of the 
equipment provided for lighting the highway 
comprising the lamps, luminaires, means of support 
and electrical and other auxiliaries. 

3.2.2 Lighting System — An array of luminaires having 
a characteristic light distribution sited in a manner 
concordant with this distribution. (Lighting systems 
are commonly designated by the name of the 
characteristic light distribution, for example, cut-off, 
semi-cut-off, etc.) 

3.2.3 Luminaire — A housing for one or more lamps, 
comprising a body and any refractor, reflector, diffuser 
or enclosure associated with the lamp(s). 

3.2.4 Outreach — The distance measured horizontally 
between the centre of the column or wall face and the 
centre of a luminaire {see Fig. 1). 

3.2.5 Overhang — The distance measured horizontally 
between the centre of a luminaire mounted on a bracket 
and the adjacent edge of the carriageway {see Fig. 1). 

3.2.6 Mounting Height — The vertical distance between 
the centre of the luminaire and the surface of the 
carriage (see Fig. 1). 



3.2.7 Spacing — The distance, measured along the 
centre line of the carriageway, between successive 
luminaires in an installation (see Fig.l). 

NOTE — In a staggered arrangement, the distance is measured, 
along the centre line of the carriageway, between a luminaire 
on one side of the carriageway and the next luminaire, which 
is on the other side of the carriage. It is not the distance 
measured on the diagonal joining them, nor the distance 
between successive luminaires on the same side of the 
carriageway. 

3.2.8 Span — That part of the highway lying between 
successive luminaires in an installation. 

3.2.9 Width of Carriageway — The distance between 
kerb lines measured at right angles to the length of the 
carriageway (see Fig. 1). 

3.2.10 Arrangement — The pattern according to which 
luminaires are sited on plan, for example, staggered, 
axial, opposite. 

3.2.11 Geometry (of a Lighting System) — The inter- 
related linear dimensions and characteristics of the 
system, namely the spacing, mounting height, width, 
overhang and arrangement. 

3.3 Photometric Terms 

3.3.1 Luminous Flux — The light given by a light 
source or a luminaire or received by a surface 
irrespective of the directions in which it is distributed. 
The unit of the luminous flux is the lumen (lm). 

3.3.2 Lower Hemispherical Flux or Downward Flux 
— The luminous flux emitted by a luminaire in all 
directions below the horizontal. 





.77/ 



/ m/ F 



o = location of columns 

h - mounting height of luminaires 

d - width of the carriage way 



p = outreach 
$ = overhang 
c = clearance 



Fig. 1 Siting of Luminaries: Characteristic Dimensions 
PART 5 OUTDOOR INSTALLATIONS 



305 



SP 30 : 2011 



3.3.3 Luminous Intensity — The quantity which 
describes the light-giving power of a luminaire in any 
particular direction. The unit of luminous intensity is 
the candela (cd). 

3.3.4 Illumination — The luminous flux incident on a 
surface per unit area. The unit of. illumination is the 
lumen per square metre (lux). 

33.5 Luminance (at a Point of Surface and in a Given 
Direction) — The luminous intensity per unit projected 
area of a surface. If a very small portion of a surface has 
an intensity / can del as in a particular direction and its 
orthogonal projection (that is, its projection on a plane 
perpendicular to the given direction) has an area D, the 
luminance in this direction is I/D candelas per unit area. 
The usual unit is the candela per square metre (cd/m 2 ). 

3.3.6 Luminosity — The attribute of visual sensation 
according to which an area appears to emit more or 
less light. It is some time called brightness. 

NOTE — Luminosity is the visual sensation which correlates 
approximately with the photometric quantity 'luminance'. 

3.3.7 Light Output — The luminous flux emitted by a 
luminaire. 

3.3.8 Light Distribution — The distribution of luminous 
intensity from a luminaire in various directions in 
space. 

3.3.9 Symmetrical (Converse Asymmetrical) 
Distribution — A distribution of luminous intensity 
which is substantially symmetrical (conversely 
asymmetrical) about the vertical axis of the luminaire. 

3.3.10 Axial (Converse Non-axial) Distribution — An 
asymmetrical distribution in which the directions of 
maximum luminous intensity lie (do not lie) in vertical 
planes substantially parallel to the axis of the 
carriageway. 

3.3.11 Peak Intensity Ratio — The ratio of the 
maximum intensity to the mean hemispherical intensity 
of the light emitted below the horizontal. 

3.3.12 Mean Hemispherical Intensity — The 
downward flux divided by 6.28 (2rc) (This is the 
average intensity in the lower hemisphere). 

3.3.13 Intensity Ratio (in a Particular Direction)